BIOLOGY: FORM ONE: TOPIC 3 - CELL STRUCTURE AND ORGANIZATION

TOPIC 3: CELL STRUCTURE AND ORGANIZATION

The Meaning of the Cell

Explain the meaning of the cell

Plants and animals are made up of units called cells. The cells are microscopic in such a way that they cannot be seen by our naked eyes. Some organisms like protozoa, diatoms and bacteria consist of one cell and are called single-celled or unicellular organisms. Some are made up of many cells and are called multicellular organisms.

The cell structure of living things was first seen by Robert Hooke in 1667 when he examined fine slices of cork. Robert Hooke believed that the cells were empty and that the cell wall and cell membrane were the most important parts of the cell but now cell contents are seen to be the most important ones. Therefore a cell can be defined as the smallest unit of living things or a cell is a basic unit of life.

The Characteristics of the Cell

Mention the characteristics of the cell

Characteristics of the cell include the following:

1. Cells are small microscopic structures which cannot be seen by our naked eyes.
2. Cells are capable of dividing by mitotic process or meiotic process.
3. Cells contain structures called organelles.

The cell theory

1. A cell is a basic unit of structure and function in living organisms.
2. New cells only come from pre-existing ones.
3. Cells contain structures called organelles.

The cell theories were proposed jointly by two scientists namely Schleiden, a Belgian botanist, in 1838 and Schwann, German Zoologist, in 1839

Difference Between Various Types of Cells

Differentiate various types of cells

Differences between cell wall and cell membrane

Cell wall	Cell membrane
It is a non–living structure	It is a living structure
It is made up of cellulose	It is made up of lipoprotein
It is freely permeable	It is selectively permeable

Different between prokaryotic and Eukaryotic cells

Eukaryotic cells	Prokaryotic cell
They have nuclear membrane	Lack nuclear membrane
Organelles are surrounded by envelopes	Organelles are not surrounded by envelopes
Have true nucleus	Have no true nucleus

The Functions of Different Parts of Plant and Animal Cells

Explain the functions of different parts of plant and animal cells

Basically a cell has three main parts

1. Cell membrane
2. Cytoplasm
3. Nucleus

Plant and Animal Cell

Draw and label plant and animal cell

Animal cell

Plant cell

Similarities and Differences of Plant and Animal Cells

Outline similarities and differences of plant and animal cells

Differences between plant cell and animal cells

PLANT CELL	ANIMAL CELL
(i) Have definite shape	Have no definite shape
(ii) Have chloroplasts	Have no chloroplasts
(iii)Have large permanent vacuoles	Have small temporary vacuoles
(iv) Centrioles usually absent	Centrioles present
(v) Have cell wall made of cellulose	Have no cell wall
(vi) The nucleus is located at the periphery	The nucleus is centrally located

Similarities between animal cell and plant cells

1. Both have cell membranes
2. Both contain cytoplasm
3. Both have nucleus
4. Both have mitochondria
5. Both have golgi bodies
6. Both have ribosomes

The Concept of Cell Differentiation

Explain the concept of cell differentiation

When most cells have finished dividing they become specialized. This means that:

• They do one particular job
• They develop a distinct shape
• Special kinds of chemical change take place in their cytoplasm

The changes in shape and chemical reactions enable the cell to carry out its special function. The process by which cells are specialized to perform a particular function is called cell differentiationor ‘division of labour’ within the organism. Similarly, the special functions of mitochondria, ribosomes and other cell organelles may be termed as division of labour within the cell.

The Importance of Cell Differentiation and Formation of Tissues, Organs and Body Systems

Outline the importance of cell differentiation and formation of tissues, organs and body systems

Humans have many different types of cells with different jobs, such as blood cells that carry oxygen and nerve cells that transmit signals to all parts of the body. Cell differentiation is the process by which cells become specialized in order to perform different functions.

Even multicellular organisms begin as just a single cell. Getting from one single cell to billions of specialized cells that perform different functions is a process that happens with the regulation of DNA and RNA. It can also be influenced by factors in the environment.

Cell differentiation holds a lot of importance for two basic reasons. Firstly, it helps to identify stem cells, which could be used in the future to deal with conditions that require transplant and form the basis of embryonic stem cell research. Also, in cytopathology, the level of cellular differentiation is used as a measure of cancer progression, where the term 'grade' is used as a marker to determine how differentiated a cell in a tumor is. Thus, the importance of this process cannot be underestimated as it could hold the key to future treatments for fatal diseases.

Difference between Cells, Tissues Organs and Body Systems

Differentiate cells, tissues organs and body systems

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