# Estimation of Cell Size | Form One - High School Biology

#### BIOLOGY REVISION QUESTIONS

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## What is a Cell?

- The bodies of living organisms are made up of small microscopic units called cells.
- A cell is the basic functional unit of an organism.

## Estimation of the Cell Size

The light microscope can be used to estimate the size of a cell. Most cells have diameters smaller than a millimeter. Due to this, cell sizes are always measures in smaller units. These are micrometres and nanometers. These units of measurements are related as shown below.

1 millimeter (mm) = 1000 micrometres (μm).
1 micrometer (μm) = 1000 nanometres (nm).

### Procedure in cell size estimation

1. One requires a microscope, transparent ruler marked in millimeters and a prepared slide of cells.
2. With the low power objective lens in place, keep a transparent ruler on the stage of the microscope.
3. Focus so that the millimeters marks on the ruler are seen as thick dark lines.
4. Estimate the diameter of the field of view by counting the one millimeter spaces between the first mark and the last one across the field of view. Count only the spaces between two thick dark lines.
5. Convert the diameter of the field of view from millimeters to micrometres.
6. Remove the ruler and place the prepared slide of cells.
7. Count the number of cells along the diameter of the field of view.
8. Calculate the diameter of one cell using the formula:

### Cell Specialization/Cell Differentiation

- This refers to the process by which a cell becomes structurally modified to perform specific functions.
- While cells have a basic outline, they become differentiated to perform specific functions.
- In particular, the root hair cell has extended surface for absorption while the sperm cell has a tail-like extension for swimming towards the ovum.

### Tissues

- A tissue is a group of cells of a particular type that are grouped together to perform the same function.

#### Tissue types in animals

1. Epithelial tissue- This is a thin continuous layer of cells for lining and protection of internal and external surfaces.
2. Skeletal muscle- This is a bundle or sheets of elongated cells with fibres that can contract. Its contraction and relaxation brings about movement.
3. Blood tissue- This is a fluid containing red blood cells, white blood cells and platelets. The main functions of blood tissue are transportation of nutrients and gases as well as protection of the body against infections
4. Connective tissue- This tissue consists of strong fibres that connects other tissues and organs thereby holding them in position.

#### Tissue types in plants

1. Epidermal tissue- This is a single thin layer of cells covering the outer surfaces. It protects inner tissues of plants from mechanical damage and infection.
2. Palisade tissue- This is a group of cells rich in chloroplasts containing chlorophyll. It has a site for the absorption of light energy and manufacture of food by photosynthesis.
3. Parenchyma tissue- This tissue consists of special thin walled irregularly shaped cells. They form packaging and storage cells.
4. Conducting tissue/Vascular bundle- This tissue consists of xylem and phloem. Xylem conducts water and dissolved mineral salts in a plant while phloem conducts food substances in solution.

### Organs

- An organ is a group of specialized tissues that are grouped together to perform a common function.
- Organs in animals include:
• Heart- Composed of connective, muscle, epithelial and blood tissues.
• Kidney- Composed of connective, epithelial and muscle tissues.
• Brain- Composed of epithelial, connective tissues.
• Lungs- Composed of epithelial, connective tissues.
Organs in plants include:
• Roots- composed of epidermal, conducting and parenchyma tissues.
• Flowers- This is composed of epidermal, conducting tissues.
• Stem- Composed of conducting, parenchyma, and epidermal tissues and palisade tissues in some cases.
• Leaves- Composed of palisade, conducting and epidermal tissues.

### Organ system

- This is a group of organs whose functions are coordinated and synchronized to perform the same function.
- Organ systems are more pronounced in animals than in plants.
- Organ systems in animals include:
• Digestive system composed of organs such as oesophagus, stomach, intestines and their associated glands.
• Circulatory system composed of the heart, blood vessels (arteries, veins, capillaries).
• Excretory system composed of kidney, liver, and blood vessels.
• Respiratory system composed of trachea, bronchus, and lungs.
• Reproductive system composed of the reproductive organs and associated glands.
• Nervous system composed of the brain, spinal cord, eye, ear organs.