CELLS

2.1 CELL STRUCTURE & ORGANISATION

Structures
YOUR NOTES

An animal and plant cell as seen under a light microscope

Structures in an animal cell visible under a light microscope

and an electron microscope

Structures in a plant cell visible under a light microscope

and an electron microscope
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STRUCTURE FUNCTION

NUCLEUS - CONTAINS GENETIC MATERIAL IN CHROMOSOMES WHICH

CONTROL HOW CELLS GROW AND WORK
YOUR NOTES
- CONTROLS CELL DIVISION

CYTOPLASM - SUPPORTS CELL STRUCTURES

- SITE OF MANY CHEMICAL REACTIONS
- CONTAINS WATER AND MANY SOLUTES

- HOLDS THE CELL TOGETHER

CELL MEMBRANE
- CONTROLS SUBSTANCES ENTERING AND LEAVING THE CELL

- GIVES THE CELL EXTRA SUPPORT AND DEFINES ITS SHAPE

CELL WALL
- SITE OF PHOTOSYNTHESIS, PROVIDING FOOD FOR PLANTS
CHLOROPLASTS
- THE CHLOROPHYLL PIGMENTS ABSORB LIGHT ENERGY
NEEDED FOR THE REACTION TO OCCUR

- CONTAINS CELL SAP

VACUOLE
- USED FOR STORAGE OF CERTAIN MATERIALS
- ALSO HELPS SUPPORT THE SHAPE OF THE CELL

STRUCTURE FUNCTION

MITOCHONDRIA - SITE OF AEROBIC RESPIRATION,

PROVIDING ENERGY FOR THE CELL
- CELLS WITH HIGH RATES OF
METABOLISM (CARRYING OUT
MANY DIFFERENT CELL REACTIONS)
WILL HAVE SIGNIFICANTLY HIGHER
NUMBERS OF MITOCHONDRIA THAN
CELLS WITH LOWER NUMBERS OF
REACTIONS TAKING PLACE IN THEM

RIBOSOMES - SITE OF PROTEIN PRODUCTION IN

PROTEIN SYNTHESIS

VESICLES - USED TO SAFELY TRANSPORT

SUBSTANCES FROM ONE PART OF THE
CELL TO ANOTHER

Specialised Cells

• Specialised cells are those which have developed certain

characteristics in order to perform particular functions. These differences
are controlled by genes in the nucleus
• Cells specialise by undergoing differentiation:this is a process by which
cells develop the structure and characteristics needed to be able to carry
out their functions
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Examples of specialised cells in animals:

STRUCTURE FUNCTION

CELL FUNCTION ADAPTATIONS

CILIATED MOVEMENT OF - EXTENSIONS OF THE CYTOPLASM AT THE SURFACE YOUR NOTES

CELL MUCUS IN THE OF THE CELL FORM HAIR-LIKE STRUCTURES CALLED
TRACHEA AND CILIA WHICH BEAT TO MOVE MUCUS AND TRAPPED
BRONCHI PARTICLES UP TO THE THROAT

NERVE CONDUCTION OF - LONG SO THAT NERVES CAN RUN TO AND FROM

CELL IMPULSES DIFFERENT PARTS OF THE BODY TO THE CENTRAL
NERVOUS SYSTEM
- THE CELL HAS EXTENSIONS AND BRANCHES, SO
THAT IT CAN COMMUNICATE WITH OTHER NERVE
CELLS, MUSCLES AND GLANDS
- THE AXON (EXTENSION OF CYTOPLASM AWAY FROM
THE CELL BODY) IS COVERED WITH A FATTY SHEATH,
WHICH INSULATES THE NERVE CELL AND SPEEDS UP
THE NERVE IMPULSE

RED TRANSPORT OF - BICONCAVE DISC SHAPE INCREASES SURFACE AREA

BLOOD OXYGEN FOR MORE EFFICIENT DIFFUSION OF OXYGEN
CELL
- CONTAINS HAEMOGLOBIN WHICH JOINS WITH
OXYGEN TO TRANSPORT IT
- CONTAINS NO NUCLEUS TO INCREASE AMOUNT OF
SPACE AVAILABLE FOR HAEMOGLOBIN INSIDE CELL

STRUCTURE
REPRODUCTION
FUNCTION
SPERM - THE HEAD CONTAINS THE GENETIC MATERIAL FOR
CELL FERTILISATION IN A HAPLOID NUCLEUS (CONTAINING
HALF THE NORMAL NUMBER OF CHROMOSOMES)
- THE ACROSOME IN THE HEAD CONTAINS DIGESTIVE
ENZYMES SO THAT A SPERM CAN PENETRATE AN EGG
- THE MID-PIECE IS PACKED WITH MITOCHONDRIA TO
RELEASE ENERGY NEEDED TO SWIM AND FERTILISE
THE EGG
- THE TAIL ENABLES THE SPERM TO SWIM

EGG CELL REPRODUCTION - CONTAINS A LOT OF CYTOPLASM WHICH HAS

(OVUM) NUTRIENTS FOR THE GROWTH OF THE EARLY EMBRYO
- HAPLOID NUCLEUS CONTAINS THE GENETIC
MATERIAL FOR FERTILISATION
- CELL MEMBRANE CHANGES AFTER FERTILISATION
BY A SINGLE SPERM SO THAT NO MORE SPERM CAN
ENTER
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STRUCTURE Examples
FUNCTIONof specialised cells in plants:

CELL FUNCTION ADAPTATIONS

ROOT HAIR ABSORPTION - ROOT HAIR INCREASES SURFACE YOUR NOTES

CELL OF WATER AND AREA OF CELL TO ENSURE
MINERAL IONS MAXIMUM ABSORPTION OF
FROM SOIL WATER AND MINERAL IONS
- WALLS ARE THIN TO ENSURE
WATER MOVES THROUGH
QUICKLY

- NO CHLOROPLASTS PRESENT

XYLEM CONDUCTION OF - NO TOP AND BOTTOM WALLS

VESSEL WATER THROUGH BETWEEN XYLEM VESSELS, SO
THE PLANT; THERE IS A CONTINUOUS COLUMN
SUPPORT OF THE OF WATER RUNNING THROUGH
PLANT THEM
- CELLS ARE DEAD WITHOUT
ORGANELLES OR CYTOPLASM TO
ALLOW FREE PASSAGE OF WATER

- THEIR WALLS BECOME THICKENED

WITH A SUBSTANCE CALLED
LIGNIN WHICH MEANS THEY ARE
ABLE TO HELP SUPPORT THE
PLANT

STRUCTURE FUNCTION
PALISADE PHOTOSYNTHESIS - COLUMN SHAPED TO MAXIMIZE
MESOPHYLL ABSORPTION OF SUNLIGHT AND
CELL
FIT AS MANY IN A LAYER UNDER
THE UPPER EPIDERMIS OF THE
LEAF AS POSSIBLE
- CONTAINS MANY CHLOROPLASTS
FOR MAXIMUM PHOTOSYNTHESIS

Cells, Tissues, Organs & Organ Systems

LEVEL DESCRIPTION

CELLS BASIC FUNCTIONAL AND STRUCTURAL UNITS IN A

LIVING ORGANISM

TISSUES GROUPS OF CELLS OF SIMILAR STRUCTURE WORKING

TOGETHER TO PERFORM THE SAME FUNCTION

ORGANS MADE FROM DIFFERENT TISSUES WORKING

TOGETHER TO PERFORM SPECIFIC FUNCTIONS

ORGAN SYSTEMS GROUPS OF ORGANS WITH RELATED FUNCTIONS,

WORKING TOGETHER TO PERFORM BODY FUNCTIONS
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STRUCTURE FUNCTION

CELL FUNCTION ADAPTATIONS

YOUR NOTES

Levels of organisation

Calculating Magnification & Specimen Size

• Magnification is calculated using the following equation:

IMAGE (DRAWING) SIZE

MAGNIFICATION =
ACTUAL SIZE

STRUCTURE FUNCTION

Rearranging the equation to find things other than the magnification

becomes easy when you remember the triangle - whatever you are trying
to find, place your finger over it and whatever is left is what you do, so:

• Magnification = image size / actual size

• Actual size = image size / magnification
• Image size = magnification x actual size
LEVEL DESCRIPTION

• Remember magnification does not have any units and is just written as
‘x 10’ or ‘x 5000’

• Let’s look at an example:

An image of an animal cell is 30 mm in size and it has been magnified

by a factor of x 3000.
What is the actual size of the cell?

To find the actual size of the cell:

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STRUCTURE FUNCTION

CELL FUNCTION ADAPTATIONS

YOUR NOTES

Using millimetres and micrometres as units

• The table below shows how millimetres are related to two other measures
of length

UNIT LENGTH IN mm

1 CENTIMETRE (cm) 10 mm

1 MILLIMETRE (mm) 1 mm

0.001 mm
1 MICROMETRE (m)

• What STRUCTURE
this basically means FUNCTION
is that 1mm = 1000μm and 1cm = 10,000μm
• This usually comes up in questions where you have two different units and
you need to ensure that you convert them both into the same unit before
proceeding with the calculation
• For example:

LEVEL DESCRIPTION
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• Remember 1mm
STRUCTURE = 1000μm
FUNCTION
• 2000 / 1000 = 2 so the actual thickness of the leaf is 2mm and the drawing
CELL FUNCTION ADAPTATIONS
thickness is 50mm
• Magnification = image size / actual size = 50 / 2 = 25 YOUR NOTES
• So the magnification is x 25 (NO UNITS)

STRUCTURE FUNCTION

LEVEL DESCRIPTION