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GROUPS OF CELLS/LEVELS OF CELLULAR ORGANIZATION:
In large organism, cells may be organized from the smallest to the biggest level as illustrated below:
Definitions:
i) Tissue: is a group of similar cells performing a particular function.
- Examples of tissues in animals are: epithelial tissue, muscle tissue, blood tissue, bone tissue, cartilage tissue, nervous tissue, connective/binding tissue etc.
- The tissues in plants are: epidermal tissue, vascular tissues (forming vessels) which include
There are so many questions to answer about the cell; fro example, what is a cell? what is its components, where are they found? how do they look like under visual aids?
by the end of this chapter, you must be able to answer all these questions.
Did you know that the following were cell??/
If you guessed, your guinness even before; they're of both plant and animal origin.
Functions of parts of cells
1. Cell membrane: allows some substances to enter and leave the cell; & keeps the cell contents together.
2. Cytoplasm: is a site for many chemical reactions in cell.
3. Nucleus: Controls all cell activities & stores the genes/genetic material/DNA RNA.
Hint: A gene is the basic unit that carries information which determines the characteristics passed from a parent to the offsprings.
4. Mitochondrion: is site for respiration.
5. Lysosomes: destroy worn out organelles/digest unwanted structures.
6. Ribosomes: site for synthesis of proteins.
Part found in plant cells only:
7. Cellulose cell wall: give plant cell support/shape/ allows H2O and dissolved substances to pass freely.
8. Chloroplast: site for photosynthesis, stores starch and chlorophyll.
9. Vacuole: stores air, water, food and waste materials/ maintains shape & firmness when turgid.
Exercise;
1. Why are cells refered to as the basic units of life?
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2. Name four structures found in both plant and animal cells.
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3. What are the differences between plant cells and animal cells?
Differences between plant and animal cells explained
Activity : Observing cells
Cells are too tiny to be seen by unaided eye. You can only observe cells using a microscope. A light microscope is an instrument used to observe things that are too small to be seen by an unaided eye. It makes them appear much larger and clearer.
Activity : Viewing an animal cell
Key question
What is found inside an animal cell?
What you need
i) prepared slides of an animal cell ii) raw egg without a shell in a clear shallow container iii) microscope iv) notebook
v) pen /pencil
What to do
1. Observe the raw egg in a dish. Identify the different layers.
i) How many layers are you able to distinguish?
ii) What is the relative position of the layers you have seen?
iii) Record the information from (i) and (ii) above in the table below. You will use it later in this activity.
2. Observe the prepared slide of an animal cell. (Ask the teacher to help you view the cell under a microscope).
3. Now compare the observation of the prepared slide with that of the raw egg.
The central part of the animal cell is called the nucleus. The fluid part surrounding the nucleus is called the cytoplasm. The outer boundary surrounding the cytoplasm is the cell membrane.
4. Draw and label the parts of the animal cell you have viewed under the microscope.
Activity;
Viewing a plant cell
All cells are similar but not identical. Although plant cells have several structures in common with animal cells, there are also some differences.
Key question
Do you know what is found inside a plant cell?
What you need
i) prepared slides of a plant cell ii) microscope iii) notebook
iv) pen /pencil
What to do
A gene is the basic unit that carries information which determines the characteristics passed from a parent to its offspring.
1. Observe the prepared slide of a plant cell. (Ask the teacher to help you view the cell under a microscope).
2. Draw only ONE plant cell you have viewed under the microscope and label its parts. The outer polygon-shaped layer is called the cell wall. The green round-shaped structures scattered in the cytoplasm are called chloroplasts.
Some parts of the plant cell may not be seen easily. The diagram below shows the parts of a plant cell.
A micrograph of an onion epidermis
A micrograph of an onion epidermis
Human cheek cells, as seen under a light microscope
Human cheek cells, as seen under a light microscope
Groups of Cells (Levels of Organisation)
Activity : Identifying the tissues in your arm
a) What is the use of your arm?
Have you ever thought about what is below the skin of your arm?
Key question
What is under the skin in your arm?
What you need
i) Notebook
ii) Pencil
iii) Pen
What to do
1. Make a sketch of your arm.
2. Try to name the parts of the arm.
3. Discuss with your neighbour the use of each part.
4. Compare your drawing with the figure below and suggest the importance of each tissue labelled.
Exercise
Identify the organsin the system shown in the figure and state the function
2. Following is a list of some functions of systems in your body. Match the functions to the corresponding system.
Tissues, Organs and Systems in Plants
A plant, like an animal is composed of tissues.
Examples of plant tissues and their functions
The xylem transports water in the plant
the phloem transports organic molecules from where they're made to where they're needed
Specialized Cells
Most of the cells in the body of an organism carryout general functions like respiration, growth and excretion. However, some cells are modified in structure to perform specific functions.
What are such cells called?
Activity : Relating the structure of specialised cells to their function
As earlier mentioned, some cells have special structures/features that enable them to carry out particular functions. In your body, a number of life processes take place, e.g. nutrition, reproduction and respiration.
For some of the life processes to be performed, specialised cells are required.
Key questions
1. What are the specialised cells in your body, and in a plant?
2. How are they adapted to their functions?
What you need
i) Notebook ii) Pencil
iii) Four sets of cards:
a. The first set is of pictures of five types of specialised cells
b. The second set has the special features of each specialised cell
c. The third set gives the functions of each specialised cell
d. The fourth set has the names of each of the specialised cells
Set one: Specialised cells
Set two: Feature/ structure of a specialised cell
- Has a tail
- Can change its shape
- Has a regular shape with many chloroplasts
- It is narrow and long providing a large surface area
- Flat biconcave shape and no nucleus
Set three: Functions of a particular specialised cell.
- To trap much sunlight to enable the cell carryout photosynthesis.
- To penetrate soil and absorb water and mineral salts.
- To provide a large surface area to absorb and carry oxygen from the lungs to respiring cells.
- To engulf foreign particles and destroy them in order to defend the body.
- To propel/swim to the egg cell and fertilise it.
Set four: Name of the cell
- Sperm cell
- Palisade cell
- Red blood cell
- Root hair cell
- White blood cell
What to do
1. In pairs, study the cards carefully.
2. Observe each specialized cell, match it with the correct statement on the card of the specialised feature and the card with the particular function.
3. Select from the list of names, the one you think matches a particular specialised cell.
4. Record your work in the table below. Present your work to the rest of the class.
Activity of Integration
You have been asked to give a talk to the Primary seven class of your former school. The talk is about importance of plants to man. The Primary seven class already knows that plants make food but they do not know the details of the structures involved in the process. Your task is to write down (in not more than 100 words) how you would explain this in your talk using your knowledge of Biology. You can use the image below during your talk
Chapter Summary
• A cell is the basic unit where most life processes take place.
• All living organisms are made up of cells.
• Cells have different shapes, sizes and structures to carryout specialized functions.
In multicellular organisms, cells combine to form tissues that join together to form organs which group to form organ/body systems.
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