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:
- Cells are small microscopic structures which cannot be seen by our naked eyes.
- Cells are capable of dividing by mitotic process or meiotic process.
- Cells contain structures called organelles.
The cell theory
- A cell is a basic unit of structure and function in living organisms.
- New cells only come from pre-existing ones.
- 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
- Cell membrane
Plant and Animal Cell
Draw and label plant and animal 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
- Both have cell membranes
- Both contain cytoplasm
- Both have nucleus
- Both have mitochondria
- Both have golgi bodies
- 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