Science form 1 chapter 2

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Chapter 2 Cell As A Unit of Life

2.1 Cells2.2 Unicellular Organisms and Multicellular Organisms2.3 Cell Organisation in the Human Body2.4 Humans are Complex Organisms

What is a cell?

1. Basic units for living things are called cells.2. All living things are made up of cells.3. A cell is the basic building unit of life. It is the smallest living unit that makes up the

organism.4. A cell is normally too small to be seen by the naked eye. Therefore we need a

microscope to see it.

Technique in using a microscope

1. Use both hands to hold a microscope – one hand holding the limb and the other supporting the base.

2. Place the microscope down gently in an upright position in a well-lit area of the room.

3. Keep the stage and other parts of the microscope clean and dry.4. Clean the lenses with tissue paper to avoid scratching them.

Chapter 2 Cell As A Unit of Life

5. Start viewing a specimen with the low power objective lens. Change to the high power objective lens if necessary.

6. Use the fine adjustment knob for focusing when using the high power objective lens.7. Always use a cover slip for the specimen when viewing through the high power

objective lens.

Cell Structure

1. Animal cell consists of a cell membrane, cytoplasm and nucleus. Small vacuoles are present in some animal cells.

2. Plant cell have a cell wall, cell membrane, cytoplasm, nucleus, chloroplasts and a large vacuole.

3. The cytoplasm and nucleus together make up the protoplasm of a cell, a semi-solid or jelly-like structure.

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Comparison between an animal cell and a plant cell

1. Both have cell membrane, nucleus and cytoplasm.2. Animal cells have small vacuoles or none at all.3. Plant cells have a cell wall, chloroplasts and a large vacuole.4. The shape of an animal cell is not fixed because it does not have a cell wall. The

shape of a plant cell is fixed because it has a rigid cell wall.

Chapter 2 Cell As A Unit of Life

Types of organisms

1. Living things are also called organisms.2. Some organisms are so large that they are easily seen.3. Some organisms are so tiny that they can only be seen under a microscope. These

organisms are called microorganisms.4. Microorganisms may be unicellular or multicellular.

Unicellular microorgamisms

1. Unicellular microorganisms are made up of only one cell.2. They can only be seen under a microscope.3. They usually live in water (aquatic).4. Some unicellular microorganisms such as bacteria and viruses live on plants and

animals.5. Unicellular microorganisms may be plants or animals.

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Multicellular microorganisms

1. Multicellular microorganisms are made up of many cells.2. They have different cells for carrying out different functions.3. Most multicellular microorganisms live in water.4. Mucor (breadmould) is a multicellular microorganisms which lives on damp bread.5. Multicellular microorganisms may be plants or animals.

Cell organization

1. A multicellular organisms has many types of cells.2. The different types of cell have different shapes and structures and carry out

different functions. We say that the cells are specialized.3. A group of cells with the same structure and function form a tissue.4. A group of different types of tissue working together to carry out a certain function

form an organ.5. A group of organs working together to carry out a certain function form a system.6. Finally, the different system will form a complete organism.

Chapter 2 Cell As A Unit of Life

Types of human cells and their functions

1. Our body is made up of different types of cells.2. Each type of cell carries out its own special functions.

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Types of tissues

1. A tissue is a group of similar cells performing the same function.2. Four examples of tissues in our body are the following:

Epithelial tissue (epithelium) It formed from epithelial cells. It forms a layer to protect the skin, and also lines the inside and outside

of various parts of the body, e.g. stomach, lungs. Muscle tissue

It is made up of muscle cells. It contracts or relaxes to cause movement. It is connected to the bones to cause strong movement. It is also connected to organs for movement, e.g. stomach, heart.

Nerve tissue It is made up of nerve cells. It detects stimuli such as pain, heat, cold, pressure and touch. It send messages ( impulses) from one part of the body to another. It is concentrated in the brain and the spinal cord.

Connective tissue There are different types of connective tissues. Connective tissue called tendons bind bones to muscles. Connective tissues called cartilage and bones support the body.

Systems in the human body

1. A system consists of organs grouped together to carry out a specific function.2. The diagrams below show a few systems and their main organs.

Chapter 2 Cell As A Unit of Life

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Organisms

1. A human being is an organism.2. A huaman being is built up as follows:

3. There is division of labour at every stage of development in the organism. Different cells perform different work. Different tissues carry out different functions. Different organs carry out different tasks. Different systems are responsible for different functions.

4. All the parts in an organism cooperate with one another to ensure that the organism functions efficiently as a whole.

Human being are complex organisms

1. Human beings are complex organisms because they have many different types of cells which are organized into tissues, organs and systems.

2. This organisation of cells enables the functions of the body to be performed separately and more efficiently. In addition, different function can be carried out at the same time by different body systems.

3. The functions of the body can performed more efficiently because the cell of an organ have special characteristics suitable for their function. For example, nerve cells have a coating that allows impulses to move very fast from one end to another.

4. In terms of brain development, human have a better developed brain compared to other living things.

5. Human have the ability to think and communicate with each other using language. They use this ability to make use of science and technology to improve themselves.