BIOLOGY Form 4 Topic 1

GROWTH
The concept of Growth
Explain the concept of growth
Growth is an increase in size/mass or growth. It is the progressive development of living thing, especially the process by which the body reaches its point of complete physical development.
The growth process is not a steady one; sometimes growth occurs rapidly, at other times slowly. Individual patterns of growth vary widely because of differences in heredity and environment.
When the rate of cell increase is higher than the rate of cell loss, growth is referred to as positive growth. When the rate of cell increase is lower than the rate at which cells are lost from the body, the organism decreases in size and weight. This is also referred to as negative growth. Several factors are known to affect growth example nutrients, temperature, light and hormones.
Internal and External Factors Affecting Growth in Plants and Animals
Investigate internal and external factors affecting growth in plants and animals
Growth in plants and animals is influenced by a number of factors, which can be grouped into two categories: internal and external.
Internal factors affecting growth in humans
These are the factors which are associated with genetic make up of an organism plus all the other processes which take place in the organism’s body. These factors include the following:
  1. Heredity:A person’s physical development is strongly affected by their genes inherited from their parents. Parent’s genes predetermine the limits of an individual’s height and other characteristics including the variability in eye colour, hair colour, body composition, and skin tone.With physical attributes such as height, parents’ genes dictate the range of height their offspring can obtain. The variability in height is a result of many external factors in the environment including nutrition and events during the child’s growth.
  2. Hormones:Human growth is affected by biochemical products such as hormones. Hormones are regarded as growth-promoting substances. Probably all the endocrine glands influence growth. Most of the hormones are secreted by the endocrine glands and play a significant role in regulating the pattern of growth and development as per instructions of the genes. Examples of these hormones and their actions are as follows:
  1. Somatotrophin:The most important hormone controlling growth from birth up to adolescence is growth hormone or somatotrophin. This is a polypeptide secreted by the pituitary. It helps in growth of bones and thereby increases the height of persons. It also causes an overall growth rate of most of tissues including brain.
  2. Thyroid hormone:This hormone plays a vital role throughout the whole period of growth. The activity of the thyroid decreases gradually from birth to adolescence. In low secretion of the hormone, skeletal maturity, dental maturity and growth of the brain are all affected. During adolescence a new phase of growth occurs under the control of steroid hormones secreted by the adrenals and gonads. The gonads of both sexes secrete estrogens in small quantities from the time of birth onwards. At puberty the oestrogen level rise sharply in girls and to a much more limited extent in boys; the sex differences is possibly due to an inhibitory hormone secreted by the seminiferous tubules of the testicle.
  3. Testosterone:Testosterone, produced by the testicle, is important in stimulating growth and it is responsible for the greater growth of muscles.
  4. Gonadotrophins:Gonadotrophins are responsible for the growth of the ovaries and testis, and later on, the secretion of estrogens and testosterone responsible for the growth and development of secondary sex characters.
External factors affecting growth in humans
Growth is also affected by external factors which include the following:
  1. Nutrients:Growth is closely related to nutrition. A sufficiency of food is essential for normal growth. An adequate supply of nutrients is naturally essential for the normal growth of humans and the need varies with the phase of development. For example: Zinc plays a part in protein synthesis and is a constituent of certain enzymes. A deficiency of zinc causes stunting, interference with sexual development and falling out of hair; Iodine is needed for the manufacture of the thyroid hormones; Bone will not grow properly without an adequate supply of calcium, phosphorus and other inorganic constituents such as magnesium and manganese; Iron is required for the production of haemoglobin; Vitamins play an important part in growth. Vitamin A is thought to be control the activities of osteoblasts. In vitamin C deficiency the intercellular substance of bone is inadequately formed. Vitamin D deficiency is the cause of rickets. Malnutrition during childhood delays growth, and malnutrition in the years proceeding adolescence delays the onset of the adolescence. Malnutrition may also result to diseases which decrease the appetite or interfere with digestion and assimilation. A majority of malnourished children fail to achieve their full genetic potential of body growth and are thus stunted or wasted or both.
  2. Diseases:Diseases are alteration of the normal body functions, disorders or morbid conditions of the mind. Diseases slow down growth in humans and other animals. A child that suffers from diseases very often is likely to have his growth stunted or retarded. Such a child may end up having a small body or deformed body parts.
  3. Cultural factors:The physical growth of human beings is definitely affected by cultural factors. Culture differs from ethnic group to ethnic group. The body growth differences correlate with varied cultural groups. The physical growth of the body follows some adaptations in different geographical areas of distribution of the groups.
  4. Socioeconomic factors:Socioeconomic influence on human growth is also a well known factor. Children from different socioeconomic levels differ in average body size at all ages. It is clear that growth of the children and adults in those families with good financial status is always good compared to the case in poor families. However, growth differences are more closely related to the home conditions than to the strictly economic status of the families.Size of family exerts an indirect influence on the rate of growth. In a large family with limited income the children do not get proper nutrition. As a result the growth is affected. The number of children in the family exerts an effect on the children’s rate of growth. Children in large families are usually smaller and lighter than children in small families. Possibly this is because in large families children tend to get less individual care and attention.
Internal factors affecting growth in plants
The internal factors that influence plant growth include following:
Hereditary factors
Heredity factors are internal factors that affect the growth of plants. They affect the physical appearance and the size of a plant
Hereditary units called genes are found in chromosomes inside the nucleus of all plant cells. These units control the various characteristics of plants such as flower colour number of floral parts, growth pattern and so on. Genes are passed from parents to off spring. For example, tall plants produce tall offspring and short plants produce short offspring.
Growth hormones
Certain hormones such as growth hormones are known to affect growth. Hormones are chemical substances that influence physiological processes. Drastic changes in their concentrations in the body will, therefore, affect growth.
There are several known growth hormones. Some of them, like auxins, cytokinins are growth-promoting while others like abscissic acid and ethylene are growth inhibitors. Most of the growth regulators are synthesized by plants while a few are synthetic in nature.The table below summarizes the role of certain plant hormones on growth of plants and seeds.
HormoneRole in plant growth
Indoleacetic acid(IAA)—the main auxin. Other three auxins seem to have rather marginal importance for plants in natural environments.
  • Promotes cell division
  • Promotes cell enlargement
  • Promotes response of shots and roots to stimuli such as light, water and gravity
  • Promote growth of adventitious roots
  • Induces parthenocarpy (formation of fruits without fertilization)
  • Causes formation of the abscission layer at the base of the leaf stalk, leading to falling of leaves (abscission).
  • Inhibits development of lateral buds, thus promoting apical dominance
  • Causes formation of callus tissue. Callus tissue forms at the site of an injury to bring about healing in the plant.
  • Controls division in the vascular cambium and xylem differentiation.
  • Used as the rooting hormones in stem cuttings.
  • 2-4 D is used as an herbicide to kill broadleaf, dicotyledonous weeds.
  • Promotes flowering in pineapples.
Gibberellins
  • Promote cell division and elongation of internodes in dwarf plants.
  • Induce parthenocarpy by initiating formation of indoleacetic acid (IAA)
  • Promote lateral bud development
  • Inhibit development of adventitious roots
  • Inhibit formation of the abscission layer on the leaf petiole
  • Promote germination of seeds
  • It helps in inducing seed germination by breaking seed dormancy and initiating the synthesis of hydrolases enzymes for digesting reserve food.
Cytokinins
  • Stimulate cell division
  • Stimulate formation of callus tissue
  • Promote flowering
  • Break seed dormancy
  • Promote formation of adventitious roots
  • Promote development of lateral buds by inhibiting apical dominance.
  • Low concentration of clytokinin induces cell elongation and causes ageing of leaves
  • Help in the production of new leaves, chloroplasts, and adventitious shoots.
  • Help in delaying senescence by promoting nutrient mobilisation.
Ethylene (ethane)
  • Promotes ripening of fruits
  • Causes formation of callus tissue, leading to falling of fruit and leaves
  • Stimulates thickening of the stem while inhibiting stem elongation
  • Helps in breaking seed and bud dormancy.
  • Promotes root-growth and formation of root hairs.
Abscisic acid (ABA)
  • induces seed dormancy by inhibiting seed germination, growth of stems, and sprouting of buds
  • Causes fruits and leaves to fall (abscission)
  • Promotes flowering
  • Stimulate apical dominance by suppressing development of lateral buds
  • Stimulates stomatal closure during water stress
Indolebutyric acidSynthetic plant hormone that promotes elongation of stems and roots
Apical dominance
An apical bud is found at the top of the plant. Apical buds are responsible for increase in plant’s height (apical growth). Lateral buds are found on the sides of the plant. Lateral buds are responsible for the formation of branches. Apical dominance is the inhibition of the growth of lateral buds by the presence of the growing apical bud. Apical dominance causes plant shoots to have a conical shape.
The apical bud produces auxins that diffuse to the lower parts of the plant. These auxins retard the development of lateral buds. The lateral branches of such a plant are short. A plant that has strong apical dominance gains more height in comparison to its width. Thus the plant assumes a conical outline.
Cutting the apex of the shoot causes the lateral buds to sprout. The dominance is overcome since the source of auxins at the apex is removed. The lateral buds sprout, branches develop, and the plant assumes an umbrella shape. Tea bushes are pruned so that they can develop many side branches. Rose plant, cypress and bougainvillea plants are pruned so that they can make a good hedge.
External factors that affect growth in plants
The external factors that affect plant growth include light, nutrients, temperature, relative humidity, water, carbon dioxide and oxygen, soil condition, biotic factors, and pollutants. Each of these factors is explained in detail below:
  1. Light:The effect of light on growth can be studied under three headings: light intensitylight quality and duration of light. Growth is generally favoured by darkness, but light is necessary because of its role in the manufacture of food. Young plants growing in the absence of light develop elongated thin stems with narrow leaves and poorly developed shoot system. Such plants are said to be etiolated.In weak intensity of light the internodes are short and the leaves are expanded. In strong intensity of light, the plant assumes a normal height. Very low light intensity reduces the rate of overall growth of the plant, by lowering the rate of photosynthesis.Growth in full spectrum of visible light is found to be better than the growth in any one of the different colours of light. Red colour seems to be the most favourable for growth.The duration of light has a pronounced effect on the growth of vegetative as well as reproductive structures. The influence of duration of light is most marked in inducing or suppressing flowering. This phenomenon is termed as photoperiodism.
  2. Nutrients:Availability, quality and quantity of food substances will automatically affect growth. For growth to occur in living things, food must be broken down to release energy. In areas where nutrients and water are adequate, competition is reduced and population increases. In case of shortage of nutrients and water, competition sets in and most individuals die.There are different mineral nutrients required for optimum plant growth. These nutrients are classified as either macronutrients or micronutrients. Macronutrients are those nutrients required by plants in high doses while micronutrients are the nutrients required in small quantities. Examples of macronutrients include nitrogen, potassium, magnesium, calcium, phosphorous and sulphur. Micronutrients include iron, zinc, molybdenum, manganese, boron, copper, cobalt and chlorine.
  3. Temperature:Atmospheric and soil temperatures are very crucial for plant growth as it affects many plant processes such as photosynthesis, metabolism, respiration, transpiration, breaking of seed dormancy, seed germination, protein synthesis, translocation, and flowering. At high temperatures the translocation of manufactured food is faster so that plants tend to mature earlier.Growth can take place between 0°C and 50°C. But the optimum temperature for the growth is between 20° and 30°C. Low temperature, however, is necessary for many plants to flower. Different physiological processes such as photosynthesis and respiration are controlled by enzymes. The enzymes are affected by temperature and pH. Enzyme activity and the rate of most chemical reactions generally increase with rise in temperature. Up to a certain point, there is doubling of enzymatic reaction with every 10°C temperature increase. But at excessively high temperatures, denaturation of enzymes and other proteins occur.It follows, therefore, that drastic changes in temperature and pH will affect growth.
  4. Relative humidity:Relative humidity (RH) is the amount of water vapour in the air, expressed as the proportion (in percent) of the maximum amount of water vapour it can hold at certain temperature. For example, an air having a relative humidity of 60% at 27°C temperature means that every kilogram of the air contains 60% of the maximum amount of water that it can hold at that temperature.The relative humidity affects the opening and closing of the stomata which regulates loss of water from the plant through transpiration as well as photosynthesis. Transpiration is slower in humid conditions. This is because diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.
  5. Water:As mentioned earlier, water is a primary component of photosynthesis. It maintains the turgor pressure or firmness of tissue and transports nutrients throughout the plant. In maintaining turgor pressure, water is the major constituent of the protoplasm of a cell. By means of turgor pressure and other changes in the cell, water regulates the opening and closing of the stomata, thus regulating transpiration. Water also provides the pressure to move a root through the soil. Among water’s most critical roles is that of a solvent for minerals moving into the plant and for carbohydrates moving to their site of use or storage. Gradual evaporation of water from the surface of the leaf near the stomata helps stabilize plant temperature.
  6. Carbon dioxide and oxygen:The oxygen and carbon dioxide in the air are of particular importance to the physiology of plants. Oxygen is essential in respiration for the production of energy that is utilized in various growth and development processes. Carbon dioxide is a raw material in photosynthesis. However, a high concentration of carbon dioxide reduces growth because of its effect on the closing of stomata, and maintenance of dormancy. If the concentration of carbon dioxide in the plant leaf is higher than the surrounding air, the stomata will open to let in more of the gas from the surrounding air so as to balance the equilibrium of the gas between the two media (air and leaf air spaces). The opposite is the case if the concentration of the gas is higher in the air than in the leaf.
  7. Soil condition:The characteristics of soil play a big part in the plant's ability to extract water and nutrients. If plants are to grow to their potential, the soil must provide a satisfactory environment for plant growth.Plant growth is influenced by the soil properties such as texture or structure, salinity, acidity, waterlogging, or compaction.
  8. Biotic factors:Diseases, plant pests, weeds and harmful substances released by roots (allelopathy) affect plant growth drastically. Weeds compete with plants for moisture, nutrients, and light. Root knot nematodes reduce absorption, so more fertilizer is necessary. All of these have negative impacts on plant growth and development.
  9. Pollutants:Pollutants can hamper plant growth. Many pollutants composed of poisonous gasses (such as carbon monoxide, sulphur dioxide, hydrogen fluoride, hydrogen sulphide) are capable of restraining growth, even bringing plants to death. Pollutants from household or industrial wastes are also able to restrain plant growth.


The Concept of Mitosis
Explain the concept of mitosis
Mitosis is the process of cell division whereby the chromosome are duplicated and distributed equally to the daughter cell.
The process of mitosis takes place in several stages, which are described below. The diagrams illustrate the stages showing a simple cell with four chromosomes.
Stages of Mitosis
Illustrate stages of mitosis
PROPHASE
This is the first stage of mitosis. In the early stages thread-like structures appear in the nucleus. These structures are the chromosomes. With time the chromosomes shorten and thicken. Then each of them splits longitudinally into two structurechromatids.Each of the chromatids is held together at a point calledcentromere.
Diagram of early prophase
As the chromosomes become visible, other events tae place. The nuclear membrane and the nucleus gradually disappear and a network of fibers appears in the cytoplasm. This network of fibers is referred to as spindle.
METAPHASE
Prophase is followed by metaphase stages. The nuclear membrane has disappeared completely by the cell and become arranged. The centromere of each pair of chromatids is attached to a spindle fiber.
Diagram of metaphase
ANAPHASE
During anaphase the centromere splits and the sister chromatids separate from each other (see figure below). Once the sister chromatids separate from each other, each is referred to as chromosome. It follows, therefore, that at this stage the chromosome number in the cell has doubled. Then the chromosomes begin to move towards opposite sides of the cell. The movement is in such a way that an equal number of chromosomes move to each pole of the cell.
TELOPHASE
Telophase begins when chromosomes reach the poles of the daughter cells. Many events in the telophase are the reverse of prophase. The chromosomes uncoil the nuclear membranes around daughter nuclei appear, the spindle apparatus break down and the nucleus reappears and nuclear membrane forms around each mass of chromosomes.
CYTOKINESIS
Telophase is followed by a stage calledcytokinesis. This is the division of cytoplasm. In plant cells a delicate membrane called a cell plate starts to form in the middle of the cell. Finally a new cell wall forms on either side of the plate. In this way, two new daughter cells are formed. In animals cells the cell membrane pinches the cytoplasm at the middle of the cell until two daughter cells are formed. Cytokinesis is completed as telophase ends.
The Significance of Mitosis in the Growth
Explain the significance of mitosis in the growth
SIGNIFICANCE OF MITOSIS IN GROWTH
  1. Mitosis results in the formation of two identical daughter cells
  2. The daughter cells are also identical to the parent cells because each daughter cell has the same number of chromosomes as that found in the original cell
  3. Mitosis enables an organism to increase in size and maintain the same number of chromosomes in its body cell
  4. Mitosis is also important for the replacement of worn out or damaged cells example in the lining of the gut and the surface of the skin
Mitosis alone does not bring about growth, when the cell divides the two daughter cells are initially only half the size of the parent cells.
The new cells must take in more materials to form the additional cytoplasm to produce fully-grown cells.
Growth and Development in Human being
Explain growth and development in human being
Growth is irreversible increase in size. It is usually accompanied by cell division. Growth can be shown by increase in mass, length, surface area and numbers. Development refers to increase in complexity and differentiation of tissues and organs.
Human growth and development are lifelong processes of physical, behavioural, cognitive, and emotional growth and change. At every stage of life, there are physical and psychological changes in the human body. The process takes many years and a person goes through many different growth stages to reach adulthood, the final stage of development. Although every person experiences growth and development uniquely, the patterns are similar for all humans as shown in the growth curve below. In this particular graph, the selected growth parameter measured is height.
The Stages of Human Post–natal Growth and Development
Explain the stages of human post–natal growth and development
Growth and development in humans can be prenatal or postnatal. Prenatal growth and development takes place in the womb before a baby is born. Post natal growth and development occurs after the baby is born.
Even though the terms growth and development are used interchangeably, there are specific differences between them. We can sum up the differences between growth and development in the following table.
GrowthDevelopment
Growth refers to increase in size, height, weight etc.Development refers to improvement in the functioning of the body process
Easily measured and observedCannot be measured easily
It is limited. Starts with birth to reach the maximum at maturityA continuous, unending process all through life.
Limited to specific areasConcerned with various aspects and parts of body and behaviour as a whole
Quantitative changeQualitative and Quantitative change
Human beings and other mammals show limited growth. Limited growth is growth that ceases at maturity. In these cases, therefore, the growth curve flattens or even declines prior to death. The decline is due to decline in smooth functioning of the organism, culminating to death. This is called senescence.
Other mammals and plants grow throughout their lives. This type of growth is called unlimited growth.
Lymph tissue grows very fast in early human life so that it produces a lot of white blood cells to fight infection (because the immune system is not able to fight infection). This type of growth in which organs grow at different rates is called allometric growth.
The post-natal period is a period beginning immediately after the birth of a child. The human post-natal growth and development may be divided into five phases or stages. These different stages of post-natal growth are summarised in the table below:
S/NoStageAge span
1InfancyFrom birth to two years
(i)NeonatalFrom birth to 4 weeks
(ii)Older babyFrom 6 to 12 months
(iii)ToddlerFrom 1 to 3 years
2ChildhoodFrom 3 to 12 years
(i)Early childhoodFrom 3 to 6 years
(ii)Late childhoodFrom 7 to 12 years or in strict sense up to the onset of puberty
(iii)Pre-adolescenceFrom 10 to 11 years
3AdolescenceFrom 13 to 19 years or in a strict sense from onset of puberty till the attainment of maturity
4AdulthoodFrom 20 to 60 years or in strict sense from attaining maturity to the age one ceases to produce one's own kind
(i)Early adulthoodFrom 20 to 40 years
(ii)Late adulthoodFrom 40 to 60 years
5Old age or ageing (senescence)From 60 years or in a strict sense from the end of the reproduction capability stage till death
NOTE: The age spans at which different stages of human growth and development occur are very confusing! So don’t stick your mind to the age spans because there are no defined ages at which each stage exactly occurs. For example, the term infant is typically applied to young children between the ages of 1 month and 12 months; however, definitions may vary between birth and 1 year of age, or even between birth and 2 years of age. The same case applies to the definition of a toddler. There is simply no consensus about what constitutes a toddler. That said, rough estimates about when toddlerhood begins vary greatly and are widely accepted in the medical literature. Some will define a toddler as an infant between the ages of 1 and 3. However, some literatures define a toddler as an infant between 1 and 2 years. Confusing!
Physiological, Psychological and Behaviour Changes Associated with Growth and Development
Explain physiological, psychological and behaviour changes associated with growth and development
In each of the above stages, various physiological, psychological and behavioural changes take place. The changes that occur in each stage are explained in detail below:
Infancy
An infant (from the Latin word infans, meaning "unable to speak" or "speechless") is the very young offspring of a human or animal. When applied to humans, the term is usually considered synonymous with baby, but the latter is commonly applied to the young of any animal. When a human child learns to walk, the term toddler may be used instead.
Infancy is a period from 0-2 years. The child undergoes physical growth at a rapid rate, greater than he will never experience subsequently. It is interesting to know the changes that take place in the first two years. Children at this stage are very active learners. During this period the baby’s physiological processes become operative and fairly well adjusted.
The infancy stage is divided into three sub-categories: (i) neonatal, (ii) older baby, and (iii) toddler.
Neonatal
Neonatal stage is the stage from birth up to 4 weeks. New babies are also called neonates.
Physical and physiological changes
  1. At this stage babies are helpless but can behave in a number of ways such as crying, moving their arms, legs and head. They can also stretch and make other movements. Baby movements are called reflexes. Examples of reflexes include moving arms, legs, and head, swallowing, and sucking.
  2. Babies at this stage suck anything put in their mouths. They can also grasp objects put in their hands.
  3. Neonates can see, but only a short distance of about 20cm. They can also hear, smell and feel. They spend most of their time sleeping.
  4. The shape of a neonate changes significantly from birth to 4 months. Initially, the head and the abdomen are bigger compared to other body parts. The body becomes proportional as the baby grows up.
  5. The immune system is immature and the baby depends on the immunity from his or her mother through breast–feeding.
  6. The baby can sit with support and can respond to sounds, for example, smiling upon hearing her mother’s voice.
  7. The rate of heart beat at this stage is very high.
Behavioural and psychological changes:Babies at this stage express their feelings mainly through crying. They cry to show hunger, thirst, pain, tiredness, fear and discomfort such as wet nappies, cold, a lot of heat, and sickness.
Older baby
This is the stage from 6 to 12 months.
Physical and physiological changes
  1. At six months a baby can completely control his/her head and sit without support. They can also roll over.
  2. At 7 months the baby learns to crawl. The baby can use his or her hands to throw and point at things he or she wants using his or her index finger.
  3. He or she can hold and drop objects and stand while holding things like tables or chairs.
  4. Teething occurs at this period.
  5. From 9 to 12 months the baby starts to walk.
  6. At this stage the sight has improved and the baby can focus on far objects and can recognize people at a distance.
Behavioural and psychological changes:The baby responds to his or her own name and other words that are familiar to him. Social development also occurs at this period. For example, at 9 months, a baby can distinguish strangers from familiar people. At 1 year, he or she understands and obeys simple commands like “come”, “go”, “stop”, etc.
Toddler
This is the age between 1 to 3 years.
Physical and physiological changes
  1. Brain develops by 90%.
  2. The rate of heart beat is reduced to about 90-110 times per minute.
  3. The child is able to control urination and defecation as urinary and anal sphincter control become possible.
  4. Immune system becomes mature.
  5. The baby can see everything that an adult can see.
  6. The baby shows sense of colour.
  7. All the 20 milk teeth appear by the age of 2.5 to 3 years
  8. Hearing has developed well.
Psychological and behavioural changes
  1. At 12 to 14 months, the child uses gestures to express his or her feelings, for example, raising arms when he or she wants to be picked up.
  2. At 15 months, the child copies what adults do. For example, a child may imitate cooking by taking a spoon and stirring it in a bowl.
  3. At 15 to 18 months, a child feeds himself or herself, addresses others with greetings, climbs onto furniture, for example bed or couch and speaks a few words.
  4. At 19 to 24 months, a child likes to play with other children (socialization), he or she can dress and undress himself or herself, run or climb steps and wants to be independent at times. He or she throws a tantrum (angry) or possibly says “No”. The child has also increased his or her vocabulary up to 50 words and starts toilet training. He or she mimics social behaviours such as holding and feeding a toy.
  5. At 25 to 36 months, a child can play with other children and share playing toys, can speak in a sentence, is more independent, can differentiate boys from girls, shows preferences such as clothes and type of toys or games and knows how to play different games. Emotionally, children may feel jealousy, for example, towards a newborn baby. They also show fear for particular things for instance fear of some insects and fear of the dark or scary noise like thunder.
Childhood
Childhood is a period from 3 years to 12 years. The stage may be divided into three stages: (i) early childhood (ii) late childhood and (iii) pre-adolescence.
Early childhood
The early childhood years, 3-6 years of age, represent a remarkable period of physical and psychological developments. It is a period when true personality begins but physical development proceeds at a slower rate. Here children become more self sufficient, acquire language, become a part of the group, become more co-ordinated and obtain a higher degree of self control. At this stage, children go to kindergarten.
Physical and physiological changes
  1. A child has good appetite and therefore grows rapidly. Good appetite is important as children at this age are very active and play a lot.
  2. The child can identify up to five colours.
  3. Motor coordination has developed well, and therefore the child can walk, jump and skip. Fine motor skills have also developed and the child can draw simple figures.
Psychological changes
  1. The child is very curious and imaginative.
  2. He or she understands right and wrong.
  3. He or she is curious about sexuality.
  4. The child can speak fluently, and can tell his or her age and name and a simple story.
Late childhood
The stage of late childhood starts from the 7th year and goes on till the 12th year. You have already gone through this period. Can you list some of the characteristics of this period?
During this period, physical growth continues at a lower rate but intellectual and emotional developments are rapid and very complex as the child moves from home to the outside world. He begins to acquire basic skills of formal learning and develops certain social activities. During the greater part of late childhood, the child’s physical growth continues, but at a slower rate until it shows a sudden spurt as the child approaches adolescence. He is more attached to his peer groups and interested in social and group activities. During this period, school tasks contribute intellectual developments too. This is the age from 7 to 9 years. At this stage children are in primary school.
Physiological and physical and changes
  1. Growth remains steady
  2. Children are very active
Psychological and behavioural changes
  1. The child can assume simple responsibilities like looking after the house when parents are not at home.
  2. The child is very social and likes to socialize and belong to groups
  3. He or she can help with household duties like washing dishes, setting the table and fetching water.
  4. The child likes to associate with peers of similar interest.
  5. This is the time children have friends and best friends. However they prefer friends of the same sex.
  6. Children at this stage can listen to peer’s opinion, but still value opinions of their parents
Pre-adolescence
This is the age from 10 and 11 years
Physical and physiological changes
  1. Growth starts to increase
  2. Appetite increases
  3. Secondary sexual characteristics start to show, for example, growth of breasts and growth of pubic hair and armpit hair.
Psychological changes
  1. Children still prefer friends of the same sex
  2. They start to become independent from the family.
  3. Children are very social and tend to value peers, opinions.
Services required to meet the needs of Children
The services required to meet the needs of a child can be categorized into two: essential or basic services, and supportive services. Essential or basic services are necessary for a baby’s survival. Supportive services are services that will help a child to grow well socially, emotionally and mentally.
Supportive services include love, care and comfort, security, and training of habits and skills. Older children need to be disciplined, trained to be independent and useful to others and be responsible.Basic services include healthy food, warmth, shelter, clothing, protection against illness and injury, exercise and rest.
  1. Healthy food:Well-balanced nutrition plays a major role in the growth of children. Healthy and well-balanced food should be given to children for good physical and mental growth.The improvement of strength, height, growth of muscle, bone tissue and body resistance is completely dependent on the diet that children eat. Children need balanced diet; they need to feed on food rich in proteins, vitamins, minerals, carbohydrates, fibre and fat in adequate proportions.Children are normally addicted to junk food, which only harms their young bodies. Bad food habits at this age can make children obese, more prone to heart diseases and other major health risks.Parents should make sure that their children are fed on energy-giving foods as well as vitamins, minerals and proteins. Children should not be provided with junk food which contains harmful cholesterol and fat that can impair the baby’s health.
  2. Protection against illness and injury:Some diseases and injuries may affect babies before they are born, at birth, or after birth. These may affect some parts of the body like the brain such that the child may become paralyzed or mentally retarded. Blindness, for instance may affect the development of physical and social capabilities of children. There are medical cases where diseases and injuries have caused a great deal of disabilities to children. Babies need to be immunized against some prevalent diseases such as tuberculosis, measles and polio.
  3. Exercise and rest:A child’s body also needs exercise. Exercise makes muscles strong. It also improves flexibility and makes the heart, lungs and other body parts work efficiently. Playing is a form of exercise. While the body needs exercise, it also needs rest. Muscles get tired when they are overworked. Sleep is a form of rest for babies. Children need enough sleep for proper growth.
  4. Warmth:Babies need warmth for proper functioning of their bodies. If babies are kept in places that are too cold, they suffer from hypothermia. If kept in too hot environment, they may develop heat rush and dehydration, and may even die. Therefore, adequate warmth is important for proper growth and development of children.
  5. Shelter:Children need a home where they can live, be nurtured, play, and be protected against harsh environmental conditions such as cold and rain. The home should be spacious, clean and safe.
Adolescence
Adolescent period follows late childhood and extends from the age of 13 to 19. Normally, girls reach adolescence earlier than boys of their age. Very often it is called the awkward age because of awkwardness, clumsiness and accompanying self consciousness which occurs frequently. During this time physical, mental, emotional and social developments are complete. It is considered as the last step in the long period of development which begins at the time of conception. By the end of adolescence, the individual is considered legally and socially matured. He is capable of living an independent life free from supervision and guidance.
Physical changes in an adolescent
During adolescence, the bodies of both girls and boys produce hormones which control many physical changes. These changes include the following:
  1. Rapid growth in weight and height.
  2. They become very energetic and active.
  3. Hair grows in armpits and groins of both boys and girls. Boys also grow beards and some grow hair on their chests.
  4. Girls start to get the menstrual flow (monthly period). Initially the flow is irregular, that is, it may not occur every month but after a few months it starts appearing every month.
  5. The breasts also start to grow bigger in girls. The monthly period onset in girl marks the puberty stage which indicates that such as person is able to become a parent. This is why girls even below 12 years of age become pregnant because they produce mature ova.
  6. Boy’s sex organs enlarge and they occasionally emit some fluid from the penis at night (wet dreams). Wet dreams indicate that the boy has reached puberty and is capable of becoming a parent. Puberty onset is the beginning of adolescent stage.
  7. Boys deepen their voice gradually while girl voices become mellow.
  8. Some adolescents (boys or girls) develop pimples (acne) on the face but the pimples clear later on.
Psychological and behaviour changes at puberty
  • Adolescence is characterized by a number of physiological, psychological and behaviour changes.
  • The changes can be a cause of conflict on one hand and positive personality development on the other hand. For example, adolescents tend to view their friends and peers as more important and influential than their parents, guardians, teachers or elders.
  • Positive personality development includes opportunity to develop various social skills, such as empathy, sharing, leadership by peers and positive influences on an individual, for instance on academic motivation and performance.
  • When adolescence is not handled properly, negative influences such as experimentation with drugs, alcoholism and stealing may occur. Susceptibility to peer pressure increases during early adolescence but it peaks at around age 14 and declines thereafter.
  • Onset of puberty is also characterized by sexuality and sexual desire. Therefore education on reproductive health is very important at this stage as adolescents may find themselves contracting sexually transmitted diseases, HIV and early pregnancies.
Personal hygiene during adolescence
  • As stated above, adolescents are very active and energetic and are thus bound to sweat a lot. It is important that they bathe daily and change into clean clothes.
  • When bathing, one must pay extra attention to genitals, armpits and areas between the toes.
  • If the armpits sweat a lot, shave the pubic hair to reduce warmth and sweating. After bathing, apply deodorant to kill germs and prevent foul smell (there are deodorant for men too). For sweaty feet, clean between the toes, dry well and, if it can be afforded, dust the areas with talcum powder. The powder absorbs the sweat, prevents bad smell and athlete’s foot.
  • In case acne strikes, it should not worry anybody. Avoid breaking the pimples but just: (i) keep the face clean; (ii) avoid applying oil creams; and (iii) avoid diet that contains a lot of oil.
  • With time, acne disappears on its own. Breaking the pimple can cause black spots or infection. If it worries the individual to a point of wishing to have it treated, it is wise to consult a doctor.
  • At this stage avoid harsh creams as they may react with the hormones and lead to damaged skin. Boys need to keep their beards shaved. Girls need to bathe more than once during the menstrual flow to avoid foul smell of blood. They need to wear sanitary towels to avoid staining their clothes with blood. The sanitary towels must be changed regularly to avoid development of foul smell and growth of germs. If commercial sanitary towels cannot be afforded, home-made pads can be prepared with cotton wool covered with gauze or just folding
Services required to meet the needs of adolescents.
Adolescents require healthy food for their growing bodies. They also require a peaceful home, security, emotional support, counselling, physical exercise and social skills that will help them resist temptations from peers and live a better and accepted lifestyle.
Adulthood
Adulthood starts at 20-60 years. It is the longest period of the life span. During this stage physical developments are fairly complete. But psychological adjustments continue throughout the entire stage. Choosing a life partner, establishing a family, becoming a useful and productive member, etc. are crucial during adulthood. One’s personality and achievements are determined by the kind of experiences he has had during his early years of life. Adulthood can be categorized into early adulthood, middle adulthood and old age.
Early adulthood
Early adulthood (also called "emerging adulthood") is a stage of life between 20 and 40 years, when adolescents become more independent and explore different life possibilities. Early adulthood is also called young adulthood stage.
Changes during early adulthood
  1. Growth has stopped, only maintenance of body parts, for example, repair of worn out cells takes place. A person may gain weight due to deposit of fats but not due to growth and development.
  2. A this stage, people are in their best physical conditions, that is very strong, energetic, have good memory capacity, sharp senses, and stamina.
  3. Performance of the body system is very high.
  4. People at this stage are very ambitious and want to succeed. They work hard to meet their goals, for example to finish studies, get a decent job and / or start a family
  5. They are selective in terms of choosing occupations or partners.
  6. They have the desire to be socially independent.
Middle adulthood
Middle or late adulthood starts at 40 years and ends at 60 years. Initially, a person is still very strong and able to do tasks that require a lot of energy.
The performance of body stems is still high. Later, in the late forties or early fifties, the rate of deterioration becomes significant. The ability to do tasks that require a lot of energy and high speed decrease, sharpness of vision decreases and memory loss may occur.
Hair starts to turn grey, skin starts to loose elasticity. Women reach menopause and their desire to have sex is reduced.
Old Age
Old age starts from 60 years and over. It is considered as the final stage of the normal life span. During this period many physical, social, emotional and behavioural changes take place. Some men and women manifest signs which are associated with old age from their 60’s onwards. These aging years demand a higher degree of emotional adjustments.
There are certain problems of adjustments such as physical and economic dependency, establishing new contacts and interests and activities to occupy increased leisure time. Psychological hazards during this stage include feelings of inferiority and inadequacy resulting from physical changes in life patterns, feeling of guilt about sitting idle and reduced income that necessitates changes in living patterns. Financial worries and ill health are common among this age.
As a person ages, various changes occurs in his or her body until her or she dies. Some of these changes are explained below:
  1. Decreased blood flow to the brain and death of nerve cells.
  2. The ability to focus on objects, smell and hear decreases.
  3. Hair turns grey as a result of reduced production of hair pigment. The hair also becomes thinner. Some men may develop a bald head.
  4. Kidney functioning slows down and the frequency of urination increases.
  5. Digestion slows down especially for those who get poor diet.
  6. Elasticity of the skin decreases. The skin gets looser and wrinkles develop.
  7. Bones may become weak, especially for those who have been taking food with less calcium in young age.
  8. Men delay getting an erection.
  9. By the age of 70, about two thirds of taste buds in the mouth die, making a person fell like food is tasteless.
The above features do not apply to all aged people. Healthy life style during young age may delay occurrence of the above features and make a person lead a normal life even in older age.A healthy life style is achieved by eating healthy food, avoiding smoking, alcoholism, overeating, drug abuse, excessive noise, toxic chemicals, stress and inactivity.
Services required to meet the needs of the elderly
Older people need healthy food to strengthen their immune system and reduce the rate of body deterioration. For very old people, the food should be soft enough for them to chew, swallow and digest.
They also need clean and comfortable clothing and a place to sleep and do light physical exercise. They need love, care, and support. Love, care and support help old people to avoid anger, loneliness and stress.
Factors which Affect the Rate of Physical Deterioration of Human Body and Services Required to Meet the Needs of an Individual at each Stage
Outline factors which affect the rate of physical deterioration of human body and services required to meet the needs of an individual at each stage
Some people may live a happy, health life up to their old age and until they die. Others get very old while they are still young.
Some of the factors affecting the rate of deterioration of the human body are psychological. They include smoking, alcoholism, drug abuse, stress and inactivity.
Some other factors are environmental. They include poor diet, excessive noise, toxic chemicals and radiations, diseases, and infections. Other factors are genetical, for example, the Werner’s syndrome.
  1. Smoking:Smokers suffer more illnesses such as cancer than non-smokers. Smoking can cause lung cancer, cardiovascular disease, Chronic Obstructive Pulmonary Disease (COPD), and stroke. Smoking leads to premature balding, skin wrinkling and osteoporosis.Osteoporosis is a condition in which bones become thin and fragile, leading to fractures, stooped posture, breathing problems and back pain.
  2. Alcoholism:The ability to metabolize alcohol decreases with age. Prolonged use of alcohol leads to damage of the central nervous system and brain and increases the risk of heart stroke and breast cancer for women.Alcoholism also increases the frequency of illnesses as it weakens the immune system and causes kidney failure and osteoporosis.
  3. Drug abuse:Drug abuse weakens the immune system and causes premature aging. It thus reduces life span.
  4. Stress:Stress may cause heart problems and high blood pressure. It also causes impairment of the immune system, thus making a person sick often. Other problems that may result from stress are failure to sleep (insomnia), fatigue, ulcers, headache and migraine.
  5. Inactivity:Sedentary work and inactivity such as spending a long time watching TV or doing office work that involves sitting most of the time results in being overweight and its associated risks. It also shortens life span.People who are inactive have more chances of developing health problems such as obesity and high blood pressure than those who are active.
  6. Poor diet:Poor diet includes both underfeeding and overfeeding. Underfeeding causes malnutrition which reduces life span. Overfeeding leads to obesity and diabetes. Obesity and diabetes cause premature aging.
  7. Diseases and infections:Pathogens produce toxins that accelerate deterioration. They also deprive our bodies of the necessary nutrients needed for good health.
  8. Chemicals and radiations:Some chemicals such as those found in cosmetics, medicines, insecticides, pesticides, foodstuffs and sprays may have adverse effects on the human body.These chemicals speed up deterioration or shorten life span. Some radiations, for example X-rays, may affect our lives by killing body cells or causing deadly diseases like cancer.
  9. Werner’s syndrome:Werner’s syndrome is a very rare disease that causes rapid ageing after puberty, such that a 20 or 30 year old person may look several decades old. It is caused by gene mutation and is named after a German scientist, Otto Werner, who described the syndrome.
The concept of seed Germination
Explain the concept of seed germination
Germination is the process by which a plant grows from a seed. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. Plant growth is said to be localized. In this case, growth is restricted to certain fixed regions like root tips and shoot tips. After the seed germinates, the embryo starts to grow as indicated in the figure below. The figure shows growth of a bean seedling between day 2 and 11.

Germination and growth of a bean seed
Changes which occur during seed Germination
Outline changes which occur during seed germination
There are changes that occur during seed germination. These are:
  1. Seed absorb water and enlarge
  2. Later on the testa bursts and the radicle emerges. The radicle continues to elongate and gives rise to many roots
  3. As the radicle elongates, the plumule is curved. At this stage, young plant is called a seedling.
Accompanying these morphological changes are chemical changes which occur inside the seed. As the seed absorbs water the foods are hydrolyzed into soluble food. The starch stored in the cotyledons or endosperm is converted to sugar by action of diastase. In some seeds, lipase catalyzes the hydrolysis of fats to fatty acid and glycerol.
It is likely that glycerol is converted into sugars since it is not detected in germinating seeds. The proteolyctic enzymes catalyze the hydrolysis of proteins to amino acids.
During germination a lot of energy is required. This energy is derived from the stored food materials.It follows, therefore that as the seed germinates its weight decreases. This is because the stored food is being used. The decrease in weight continues until the seedling is capable of photosynthesizing.
Parts of a seed
A seed is a structure formed after the fertilization of an ovule. A seed contains the embryo of the plant. The embryo grows and develops into a mature plant which produces more seeds. The embryo is made up of the plumule, radicle and cotyledons. The plumule develops into a shoot. The radicle develops into a root. The cotyledons have nutrients which are utilized by the seed during germination.
Seeds have either one or two cotyledons. A seed with one cotyledon is called a monocotyledonous seed. Examples of monocotyledonous seeds are maize, rice, millet and wheat. A seed with two cotyledons is called a dicotyledonous seed. Examples are beans, peas and groundnuts
Seeds sometimes have additional nutrient tissues in form of the endosperm. The seed coat, also called testa, encloses the fertilized ovule. The testa has a pore called the micropyle. The micropyle allows water and air to get in and out of the seed.
On the testa is a scar called the hilum. The hilum marks the point of attachment to the funicle. The funicle attaches the seed to the placenta on the ovary wall.The plumule has small leaves. The leaves are the replica of natural leaves. A radicle is a replica of a mature root. The testa is hard and encloses the seed, hence protecting it.
The figures below show the parts of a monocotyledonous seed (maize) and a dicotyledonous seed (bean).
Conditions necessary for seed Germination
Investigate conditions necessary for seed germination
Seeds require certain conditions for them to germinate. These conditions are water, oxygen, optimum temperature and light.
Water
Water is a solvent required for enzymatic activities. Water enters the seed through the micropyle. The water softens the testa thus allowing the seed to take in water. The osmotic pressure in the seed causes water to enter the seed by osmosis. Pressure is created in the swollen seed, rupturing the softened testa.
The seeds require water for the processes outlined below:
  1. Activation of enzymes: When seeds are formed, most plants store a food reserve with the seed, such as starch, proteins, or oils. This food reserve provides nourishment to the growing embryo. When the seed imbibes water, hydrolytic enzymes are activated and break down these stored food resources into metabolically useful chemicals.
  2. Most seeds need enough water to moisten them. The uptake leads to the swelling and the breaking of the seed coat, which enables the embryo to emerge from the cotyledon(s).
  3. Water is used to dissolve food substances. The food needs to dissolve so as to diffuse or get transported to the growth parts of the embryo in the seed.
  4. Water is needed for the development of the cell sap vacuoles. Large cell sap vacuoles contribute to the increase in the size of cells, hence, growth.
Oxygen
Oxygen is required by the germinating seed for metabolism. It is used in aerobic respiration, the main source of the seedling's energy until it grows leaves. Respiration produces energy for processes like cell division and transport of food to growing regions.
Oxygen diffuses into the seed through the micropyle. The softened testa later allows oxygen to diffuse directly into the tissues.
Optimum Temperature
Temperature affects cellular metabolic and growth rates. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above 16-24 °C.
Temperature is an important requirement for activation of enzymes. The enzymes in the seed work best at optimum temperature since they are denatured by high temperatures and inhibited by extremely low temperatures.
Some seeds may require to be first exposed to low temperatures before they can germinate. This is usually the case in plants that grow in temperate climates. The seeds need to go through winter before the onset of spring when the seeds germinate.
Light
The requirement of light for germination varies from plant to plant. Some plants need darkness while others need light in varying degrees.
Light or darkness can be an environmental trigger for germination and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for growth of the seedling.
Types of seed germination
There are two types of seed germination namely, hypogeal germination and epigeal germination.
Epigeal germination
Epigeal germination is a type of germination in which the cotyledons are brought above the soil level. This type of germination is seen in many dicotyledonous plants, such as beans, sunflower, castor, bean, etc. Some monocotyledonous plants such as the onion also show epigeal germination.
In a dicotyledonous seed, the plumule and radicle are attached to the two cotyledons. The hypocotyl elongates rapidly raising the cotyledons into the air. The hypocotyl is the region of the stem beneath the cotyledons and directly above the young root of a seedling. The epicotyl is the region of the shoot of a seedling which is found above the cotyledon of an embryo.
The seed absorbs water and softens the testa. The cotyledons swell and rupture the testa. The radicle elongates and emerges through the seed coat. Roots develop from the radicle. The hypocoty elongates rapidly and develops a curvature. The curved part emerges above the soil. The hypocotyl eventually straightens, raising the cotyledons and the plumule above the soil. The cotyledons are also referred to as seed leaves.
The cotyledons enlarge and turn green to carry out photosynthesis. The epicotyl elongates thus increasing the height of the seedling. The first foliage leaves emerge. The cotyledons shrivel as the stored food materials are used up. The first foliage leaves enlarge and start carrying out photosynthesis.

Epigeal and hypogeal germination
Hypogeal germination
Hypogeal germination is a type of germination in which the cotyledons remain underground. It occurs in plants such as maize, pigeon peas, wheat, etc.
The part of the embryo that elongates is the epicotyl. The epicotyl elongates rapidly, raising the plumule above the soil. The cotyledons remain below the ground level.
The shoot is pushed through the soil particles. In maize, the plumule sheath, known as the coleoptile, protects the plumule. The coleotile grows towards light.
The foliage leaves emerge through the split end of the coleoptile. The foliage leaves carry out photosynthesis. The radicle is protected as it emerges through the maize grain by a sheath called coleorhizae.
Practical activities to demonstrate Epigeal and Hypogeal Germination
Carry out practical activities to demonstrate epigeal and hypogeal germination
Growth regions of a seedling
The growth of the radicle and the plumule causes the elongation of a seedling. A radicle develops and forms the roots, while a plumule develops and forms the shoot. The rate of growth can be measured at the tip of the root or shoot.
Cells at the root and shoot apices have a high capacity to divide. The dividing cells are called meristematic cells. The cells make up a tissue called the apical meristem. These cells rapidly undergo mitosis, thus enlarging and giving rise to more cells.
The very cells increase the size of the shoots and roots. The cells differentiate to form tissues that carry out specific functions.
The plant organs elongate, resulting in growth at the root and shoot apices. This type of growth is known as primary growth.
The meristematic tissue at the shoot apex actively divides, leading to the elongation of the shoot. The meristematic tissue also gives rise to leaves. Leaf primordia, from which the leaves develop, occur at the nodes of the shoots.
The part of a stem between one node and the next is called the internode. The axillary bud has meristematic tissue known as the intercalary meristem. The meristem tissue brings about internode elongation.

How a plant grows from a seed