O level Biology-Cell structure and Organisation

What are cells?

• A cell is a basic unit of life as it is the simplest unit which makes up a living thing

• Cells take in raw materials and process them to make new molecules. They either use these new molecules or transport them to other parts of the body

• Most cells are too small to be seen with our eyes alone

• Light and electron microscope allows us to see cells and their parts

Light microscope

• A light microscope magnifies an object up to 1000 times its original size and produces coloured light micrographs

• Cell wall, cytoplasm, chloroplasts, mitochondria, vacuoles can be seen with light microscope

Electron microscope

• An electron microscope magnifies an object up to 200000 times its original size and produces

• Electron micrographs can be artificially colourised

• Cell membrane and ribosomes can be seen with electron microscope

What is protoplasm?

Protoplasm [ complex jelly-like substance ] is the living material found in a cell. The protoplasm of a cell is made up of the cell membrane, nucleus, cytoplasm and vacuole.

Cell wall ( present only in plant cells )

Description:

• Outermost part of the cell

• Made up of cellulose

• Fully permeable to small molecules

Function:

• Protects the cell from injury

• Gives the cell its shape

Cell membrane

Description:

• Partially permeable membrane that surrounds the cytoplasm

• Made up of lipids and proteins

Function:

• Controls substances leaving or entering the cell

Cytoplasm

Description:

• Jelly-like substance embedded with special structure called organelles

Function:

• Each organelle is specialised for a specific function

• Site where most cellular activities occur

Nucleus

Description:

• Surrounded by a membrane called the nuclear membrane

• Contains genetic material in the form of chromosomes

Function:

• Controls cell activities such as growth and repair

• Important for cell division

Mitochondrion ( Many: Mitochondria ) (Powerhouse)

Description:

• Small oval/ sausage shaped structure

• Enclosed by a double membrane

• Inner membrane is highly folded

Function:

• Site where most aerobic respiration occurs

• Provides energy for cell activities like growth and reproduction ( when glucose is broken down in the presence of oxygen during aerobic respiration )

Ribosomes ( the tiny dots )

Description:

• Small round structures

• Found freely throughout the cytoplasm or attached to organelles in the cell

Function:

• Synthesise proteins in the cell

Vacuole

Description:

• Fluid-filled space

• Large and central in plant cell; enclosed by a partially permeable membrane and contains cell sap

• Small and numerous in animal cells: enclosed by a membrane and exist temporarily

Function:

• Cell sap in plant vacuoles contain dissolved sugars, mineral salts and amino acids

• Vacuoles in animal cell store water and food substances

Chloroplast

Description:

• Oval structure

• Contains a green pigment called chlorophyll which is contained in stacks of membranes

Function:

• Site for photosynthesis ( process by which plants make food )

• Chlorophyll is essential for photosynthesis

What are specialised cells?

Specialised cells are cells that have gone through differentiation. They develop special structures or lose certain structures to enable them to carry out specific functions

Red blood cells

Cell structure and function:

• Transports oxygen to all parts of the body

Adaptation to function:

1. Contains haemoglobin ( a red pigment )

• Transports oxygen

2. Circular bioconcave shape

• Increases surface area- to- volume ratio which increases the rate of oxygen diffusion

3. Flexible and can squeeze through small blood vessels

4. Nucleus is absent

• increases amount of haemoglobin carried

Root hair cell

Cell structure and function:

• Absorbs water and mineral salts from the soil

Adaptation to function:

1. Long and narrow root hair extension

• Increases surface area- to- volume ratio which increases rate of absorption or water and mineral salts

Muscle cell

Cell structure and function:

• Causes muscle contractions to produce movement

Adaptation to function:

1. Contains many mitochondria which provide energy for muscle contractions

What is a tissue?

A tissue is a group of similar cells working together to perform a specific function

Simple tissue

A simple tissue consists of cells of the same type

Complex tissue

A complex tissue consists of more than one type of cell

Others…

• Different tissues may combine together to form an organ

• Organs work together in organ systems. The digestive system is an example of an organ system which involves organs such as mouth, oesophagus, stomach, small intestine, large intestine working together to digest food

• A multicellular organism is made up of many organ systems working together

Levels of organisation in a multicellular organism

cells→tissue→organ→organ system→organism