2.1 What is a Cell?
Cells are the basic units of all living things. Animals are made up of cells. Plants are made up of cells. You and I are made up of cells.
Basically, cells:
- are the building blocks of life.
- can function on its own.
- are responsible for carrying out life processes.
Parts of a Microscope
Sometimes in the examinations, there might be questions on parts of the microscopes .
Functions of the parts:
- Eyepiece- To observe and magnify the image of specimen.
- Body tube- To hold the eyepiece at a fixed distance from the objective lens.
- Objective lens- To magnify the specimens.
- Stage- Where the slide is placed.
- Stage Clips- To hold the slide in place.
- Diaphragm(Dye-a-fram)-Controls the amount of light entering the objective lens.
- Coarse adjustment knob-To raise/lower the objective lens for a rough focus.
- Fine adjustment knob-To slightly change the position of objective lens for a sharper focus.
- Light source-Provides light into the specimen slide.
- Arm & Base-Hold and support the microscope.
1. A cell consists of a cell membrane(plasma membrane) surrounding a living component called the protoplasm.
The Functions of Cell Structures
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| Animal Cell |
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| Plant Cell |
Functions of the parts
- Nucleus-Controls all the cellular activities.
- Cell membrane(Plasma membrane)-Encloses the cytoplasm,controls movement of substances in and out of cell.
- Cytoplasm(Site-o-plas-m)-A jelly-like medium for chemical reactions that contains water and substances.
- Cell wall(only in plants)-made up of cellulose, gives shape to the cells.
- Vacuole(only in plants)-Stores water and other substances like sugar and salt, supports the plant when its full of water.
- Chloroplast(only in plants)-Contains chlorophyll(green pigments) that absorbs light for photosynthesis to produce food and oxygen.
Comparison between Animal Cells and Plant Cells
2.2 Unicellular Organisms and Multicellular Organisms
Living things are also known as organisms.
Unicellular organisms:
-Are organisms that consists of only one cell.
Unicellular organisms:
-Are organisms that consists of only one cell.
-Are also known as unicellular microorganisms, due to their small size.
-Can carry out all life processes.
-Most unicellular organisms live in water/moist places.
-Examples of unicellular organisms are:
Multicellular organisms:
-Are organisms which consist of many cells(i.e more than one).
The cells are of many types.
The cells are of many types.
-Each type of cell is specialised in carrying out specific life processes.
-Some are smaall and can only be seen under the microscope, but most are big and clearly visible.
-Example of multicellular organisms are:
2.3 Cell Organisation in the Human Body
The human body has billions of cells. The human beings are the most complex multicellular organisms. Different types of cells have different shapes, sizes, structures to perform different functions. This is known as cell specialisation. This specialisation allows organisms to perform various life processes efficiently.
The human body has billions of cells. The human beings are the most complex multicellular organisms. Different types of cells have different shapes, sizes, structures to perform different functions. This is known as cell specialisation. This specialisation allows organisms to perform various life processes efficiently.
The Types and Functions of different Cells in the Human Body
- Nerve cell-Has long thin fibres which conduct nerve impulses throughout the body.
- Muscle cell-Can contract and relax to produce movement.
- Red blood cell-A biconcave disc shaped cell without a nucleus that transports oxygen throughout the body.
- White blood cell-Can change shape to kill bacteria.
- Sperm cell-Male reproductive cell that has a long tail which enables it to swim towards the ovum.
- Egg cell(Ovum)-Female reproductive cell which is the largest cell in the human body(0.1mm).
- Epithelial cell-Lines the cavities in the body and also cover flat surfaces.
Organisation of Cells in Multicellular Organisms
From cells to tissues
Similar cells are arranged in groups to form tissues. Every cell in a tissue has the same structure and carries out a similar function. The human body has four main types of tissues:
Connective tissue- As it name suggests, it connects different sets of tissue, also provides support. Example: Blood, bone, adipose tissue, tendon, ligaments and cartilage.
Nervous tissue-Consists of nerve cells which responds to stimuli and conduct nerve impulses.
Muscle tissue-contracts and causes body movement.
Epithelial tissue-Covers the body and lines all organs.
From tissue to organs
A group of different tissue make up and organ. Different types of tissues in an organ perform different functions but they all work together in the organ which in turn carries out one / more functions.
Brain-consists of nerve tissues and connective tissues. It controls various body systems.
Lungs-consists of epithelial, connective, muscle, and nervous tissues. They perform respiratory functions.
Heart-consists of connective, muscle, and nerve tissues. It pumps blood to all parts of the body.
Stomach-consists of epithelial, connective, and muscle tissues. It digests and breaks down food.
m organs to systems
m organs to systems
A group of organs work together to form a body system that performs a specific function.
- Skeletal system-provides supporrt and protects internal organs
- Muscular system-contraction of muscles produces movements.
- Circulatory system-Transports nutrients and oxygen to cells. Transports waste products to excretory organs.
- Digestive system-Digests and absorvs food. Eliminates undigested food.
- Excretory(urinary) system-removes excretory products from the body.
- Nervous system-receives stimuli, produces nerve impulses and coordinates responses.
- Reproductive System-Produces offsprings.
- Lymphatic system-Defends body against infections.
- Endocrine system-Produces hormones . Controls and coordinates body activities.
- Respiratory system- Inhales oxygen and exhales carbon dioxide.
2.4 Human Beings are Complex Organisms
- The human being is a complex organism because it is made up of billions of cells.
- The organism is able to perform various processe because of specialisation of cells.
- The process in which each type of cell is specialised to perform specific function is known as division of labour.
- Division of labour among cells, tissues, organs and systems ensure that the organism functions efficienntly.
-End of chapter-
Examples of some organs and their functions: