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CELLS
what is a cell? What are the types of cells? What are their functions? Can we view them?
By the end of this chapter, you should be able to learn:
• what a cell is.
• identification of the parts of a typical animal cell and plant cell and their functions.
• explain the structure of specialized cells in terms of their functions in an organism.
• distinguish the levels of cellular organisation.
INTRODUCTION
Have you ever wondered what organisms are made of?
Imagine if a house was carefully dismantled. What would you see piled up as the smallest components that were joined to construct the house? You will notice that they were the bricks/blocks that were joined several times in different ways to form a house. Likewise, organisms are made up of tiny building blocks of life that are called cells. The cells are organized at different levels to perform specific functions. The knowledge you will acquire about cell structure and organization will enable you to explain how an organism interacts with its environment to sustain its life. This same knowledge has enabled scientists to make important medical and agricultural advances in science.
Animal and Plant Cells
Activity;
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
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
Test: ask your friend whether the following are cells.
Functions of the Parts
Cell membrane: This is a thin, outer layer surrounding the contents of the cell. It allows some substances to go in and some to come out of the cell.
Cytoplasm is a mucus-like liquid in the cell. This is where some of the life processes take place.
Nucleus is the “brain” of the cell. It controls all the chemical activities that take place in a cell. This is because of the presence of genes that carry instructions and information on how the activities should occur.
a chicken egg
a sperm cell
sperm fertilizing an egg
Groups of Cells (Levels of Organisation)
In large organism, cells may be organized from the smallest to the biggest level as illustrated below:
Cells - Tissue - organ - organ system - organism.
tissue
tissue
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.
organ level
organ level
Organ: is a group of different tissues performing a particular function. Example of animal organs: heart, eye, ears, nose etc.
Examples of plant organs are: stem, leaf, root, flower and fruit.
organ system
organ system
Organ system: is a group of different organs performing a particular function There are two systems in plants: root and shoot systems. Examples organ systems in animals are: circulatory system, digestive system, excretory system etc
complete level of organization in a rat
complete level of organization in a rat
Did you realise that the rat has got the same levels of organization like a human being??
Do plants have the same levels of organization?
Lets enter the lab and navigate this fascinating science
BIO 2101 T.S through a leaf.docx
plant tissues
plant tissues
The tissues in plants are: epidermal tissue, vascular tissues (forming vessels) which include
Xylem which Transports water and minerals while Phloem Transports food materials.
The organs in plants are: stem, leaf, root, flower and fruit.
i) Several leaves form a food making system for the plant.
ii) Flowers make up the reproductive system of a flowering plant.
iii) After fertilization, the flower changes into a fruit which is a food storage organ. The fruit bears seed that can grow into new plants.
iv) The stem is the organ consisting of vessels which transport water and mineral salts from the ground to the upper parts of the plant. The stem also transports food from the leaves to other parts of the plant.
v) The root is an organ for absorption of water and mineral salts from the soil into the plant. Some roots e.g. the carrot and sweet potato store food nutrients.
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?
can you state the function of each??
can you state the function of each??
but how can you observe cells??
but how can you observe cells??
Have you heard of microscope? what of hand lens?
Do you know where each of these magnification aids are use??
Observe the doctor use a microscope too.
A microscope is an instrument used to observe things that are too small to be seen by an unaided eye by making them appear much larger and clearer. There two types of compound microscopes
1. Light microscope: uses a light beam to work.
2. Electron microscope: uses an electron beam to work.
- Base: provides firm support to the microscope of a flat surface.
- Body tube (barrel or ocular tube): holds the eyepiece and the revolving nose piece.
- Coarse adjustment knob: raises or lowers the body tube through longer distances to bring the image into initial focus.
- Fine adjustment knob: raises or lowers the body tube through smaller distances to bring the image into sharper focus. It is mostly used with the high power objective lens.
- Diaphragm: is an aperture that regulates the amount of light passing through the condenser to illuminate the specimen
- Eye-piece (ocular lens): contains a lens which contributes to the magnification of the specimen under view. It further magnifies the image formed by the objective lens.
- Objective lens: bring image into focus and magnifies it.
- Mirror: reflects light through the condenser to light up the
- Revolving nose piece: holds the objective lenses in place and enables the change from one objective lens to the other
- Condenser: concentrates light on the object on stage
- Stage: flat platform where the microscope slide is placed.it has two clips to hold the slide into position
Magnification of a microscope and drawings:
By definition magnification is the number of times the size of the drawing multiplies the size of the specimen from where it has been drawn. Magnification should be written at the bottom of the drawing with a multiplication sign infront of a number and it has no units since it’s a ratio. Magnification can be calculated as below depending on whether the drawing is taken with necked eyes or hand lenses or light microscope
Magnification1. Total Magnification of microscope = magnification of the eye piece lens X is the number of times the image of specimen is larger compared to real size of the specimen. Fmagnification of the objective lens or a compound light microscope,
Magnification of a drawing obtained with an unaided eye or hand lens 2.
= size (length or width) of a drawing
Size (length or width) of the object
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
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