Cells and cell specialisation
Cells are the basic building blocks of any living organism. They carry out all the processes necessary for the survival of the organism. Plants and animals are made up of thousands or millions of microscopic cells.
- Cells contain cytoplasm enclosed in a cell membrane.
- Many chemical reactions take place in the cytoplasm to keep
the cell alive.
- Most cells have a nucleus which controls the chemical reactions in the cell and cell division.
- Only plant cells have a cellulose cell wall and a large central vacuole.
- Cells are often specialised to carry out particular tasks.
Components of a cell
The diagram below shows some components of a plant cell:
- a jelly-like enclosed by the cell membrane
- it contains the cell organelles, e.g. mitochondria, nucleus
- cell chemical reactions take place in the cytoplasm.
- Non-living structure made of cellulose.
- Found in plant cells only
- Prevents plant cells from bursting
- Allows water and salts to pass through (freely permeable)
- a partially permeable boundary around the cytoplasm
- it prevents cell contents from escaping and controls what substances enter or leave the cell
- Contains cell organelles.
- Food substances.
- Mostly H2O.
Semi-permeable, partially permeable or selectively permeable is term used to describe a material that allows certain substances to pass through it whilst blocking others.
- it is a fluid-filled space surrounded by a membrane
- contains mostly water.
- it is found inside the cytoplasm of plant cells.
- also contains salts and sugars.
- helps to keep plant cells firm.
- is a circular or oval structure containing DNA in the form of chromosomes
- it is found inside the cytoplasm
- controls all activities of a cell.
- Contains green pigment called chlorophyll which is important for doing photosynthesis.
Plant and animal cell structure
A living organism is made up of different types of cells which carry out specific functions. Each cell is dependent on the other and together they support the diverse processes in an organism. For example, for muscles cells to respired and produce energy they use oxygen which is provided by the red blood cells, as illustrated by the diagram below:
- Arrow 1 indicates the direction of movement of carbon dioxide.
- Arrow 2 indicates the direction of movement of oxygen.
In order for cells to be able to perform a particular specialised task, they develop a distinct shape and structure. The changes in shape and structure of a cell enables the cell to efficiently carry out its special function.
When cells are specialised:
- they do one particular job
- they develop a distinct shape
- special kinds of chemical change take place in their cytoplasm.
Examples of specialised cells are:
- Red blood cells
- Muscle cells
- White blood cells
- Nerve cells
- Palisade cells
- Root hair cells
Red blood cells
Function of red blood cells
Red blood cells transport oxygen from lungs to body tissues.
How the red blood cells are specialised for their function
- they lack a nucleus into order to increase their oxygen carrying capacity.
- their bi-concave shape increases the surface area for the absorption of oxygen.
- they are flexible to allow them to pass through the narrow walls of the capillaries.
- they contain a red pigment called haemoglobin which carries oxygen needed for cell respiration to produce energy.
Function of the muscles cells
Muscle cells are responsible for contraction to produce movement in animals.
How the muscle cells are specialised for their function
- They have the ability to change their shape and contract when stimulated by an electric impulse from the nerves.
Palisade mesophyll cells
The diagram below shows the structure of a palisade cell:
These are found underneath the upper epidermis of the leaves.
Function of palisade cells
Palisade cells are responsible for making food during photosynthesis.
How the palisade cells are specialised for their function
- contains large number of chloroplasts that contain chlorophyll, an enzyme required for photosynthesis.
- They are elongated in shape and closely packed to increase surface area for absorption of sunlight and carbon dioxide.
Root hair cells
Function of root hair cells
Root hair cells are responsible for absorption of water and salts from the soil.
How the root hair cells are specialised for their function
- Have thin cell walls to allow water and nutrients to pass easily from the soil.
- They have hair like projections to penetrates between the soil particles and offers a large absorbing surface area.
- Have large vacuoles for water absorption and storage.
Similarities and differences of plant and animal cells
Differences between plant cells and animal cells
- Only plant cells have chloroplasts.
- Plant cells have a large central vacuole while some animal cells have small vacuoles and some doesn’t have any.
- Only plant cells have a cell wall.
- Plant cells have a regular shape while animal cells have irregular shapes.