4.1.1 Cell structure

Functions of organelles

Organelle Function Plant or animal

NucleusContains genetic material, which controls

the activities of the cellBoth

CytoplasmMost chemical processes take place here,

controlled by enzymesBoth

Cell membraneControls the movement of substances into

and out of the cellBoth

Mitochondria Most energy is released by respiration here Both

Ribosomes Protein synthesis happens here Both

Cell wall Strengthens the cell Plant ONLY

ChloroplastsContain chlorophyll, absorbs light energy

for photosynthesisPlant ONLY

Permanent vacuole

Filled with cell sap to help keep the cell turgid

Plant ONLY

All living things are made up of cells. The structures of different types of cells are related to their functions.

Prokaryotic cellsBacteria

Comparing Prokaryotic and Eukaryotic

Prokaryotic Eukaryotic

No membrane bound nucleus Membrane bound nucleus

DNA is single stranded DNA is double stranded

May contain plasmids Do not contain plasmids

Smaller Larger

Eukaryotic cells

Standard form

Keywords

Keyword Definition

Unicellular Single celled organisms

Multicellular Organisms that consist of more than one cell

Prokaryote A unicellular organism that has no membrane bound organelles

Eukaryote A cell from any organism that contains membrane bound organelles, can be multicellular or unicellular.

Organelle Structures found within cells that have specialised functions

Membrane bound organelle

Organelles found within cells that have specialised functions and are surrounded by a plasma membrane e.g chloroplast, mitochondria, nucleus.

4.1.1 Cell structure Cells are specialised for a particular function. Structure helps them to carry this function out.

Specialised Cells

Cell Diagram Function Adaptations

Sperm cell Transport the male DNA to the female DNA.

Long tail – to swim.Lots of mitochondria – for energy.

Enzymes in head – to digest egg cell membrane

Nerve cell To carry electrical signals from one part of the body to another.

Long – to cover distance.Branched connections – to connect to other nerve cells.

Muscle cell To contract quickly. Long – so that they have space to contract.Lots of mitochondria – to generate energy for the contraction.

Root hair cells

To absorb mineral ions and water from the soil.

Long hairs – to stick into soil.Big surface area – to absorb more water and mineral ions.

Xylem cells To transport water in plants. Hollow in the centre – to allow water to flow through.

Phloem cells

To transport food in plants. Very few subcellular structures – to allow food to pass through.

Cell differentiation• Differentiation is the process by which a cell changes to become

specialised for its job.• As cells change, they develop different subcellular structures and

turn into different types of cells.• In most animal cells, cell differentiation mostly occurs when the

baby develops in the womb• Plant cell contain meristem tissue at the roots, buds, shoots and

tips and these retain the ability to differentiate throughout the life of the organism

• The cells that differentiate in mature animals are mainly sued for repair and replacing cells (e.g. skin or blood cells).

• Differentiation is caused by genes being switched on and off.• Undifferentiated cells are called STEM CELLS, and can give rise

many more cells of different types from which certain other cells

can arise from differentiation.• In some countries stem cell research is banned. In the UK it is

allowed as long as it follows strict guidelines

Arguments for and against the use of STEM cells

For Against

Adult Stem cells come from bonemarrow and can replace faulty blood

cells.

Adult stem cells can only differentiate into a small number of different cells so

cannot treat all illnesses

Embryonic stem cells could replaces faulty cells in sick people and help cure

disease. E.g diabetes

Embryonic stem cells shouldn’t be used as each embryo is a potential human

life which has to be destroyed.

Embryos are usually from fertility clinics, they are embryos not used in IVF

Adult stem cells have to be removed during an operation which is painful

Therapeutic cloning – embryo could be made to have the same genetic

information as the patient so they wouldn’t be rejected by the body

The use of stem cells has potential risks such as transfer of viral

Infection.

4.1.1 Cell structure

𝑚𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 =𝑠𝑖𝑧𝑒 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒

𝑠𝑖𝑧𝑒 𝑜𝑓 𝑟𝑒𝑎𝑙 𝑜𝑏𝑗𝑒𝑐𝑡

Microscopes let us see things we cannot see with the naked eye.

Comparison of light and electron microscopes

Light microscopes Electron microscopes

Use light and lenses to form an image of the specimen and magnify it.

Use electrons instead of light to form an image.

Can see individual cells and larger subcellular structures (e.g. nuclei).

Can see smaller structures in more detail (e.g. ribosomes, plasmids and

the internal structures of mitochondria and chloroplasts)

Lower resolution, due to light having a longer wavelength.

Higher resolution, due to electrons having a shorter wavelength.

Lower magnification. Higher magnification.

Can see living samples Samples must be dead

Resolution – the ability to distinguish between two points, the better the resolution the more detail can be seen in an image

Looking at your slide (using a light microscope)1. Clip slide onto stage.2. Select lowest-powered objective lens (lowest magnification).3. Use the coarse adjustment knob to move the stage up to just below

the objective lens.4. Look down the eyepiece. Use the coarse adjustment knob to move

the stage downwards until it is roughly in focus.5. Adjust the focus with the fine adjustment knob until you get a clear

image.6. If you need greater magnification, swap to a higher-powered

objective lens.

Converting Units

cm mm µm nm

x 10 x 1000 x 1000

÷ 10 ÷ 1000 ÷ 1000

Calculating magnification from an image

• Measure the line on the image in mm• Multiply the measurement by 1000• Divide by the actual size - this will be given in the information

Calculating actual from an image

• Measure the line on the image in mm• Multiply the measurement by 1000• Divide by the magnification - this will be given in the information

Calculating magnification from a scale bar

• Measure the scale bar in mm• Multiply the measurement by 1000• Divide by the actual size - the number underneath the scale bar.

Preparing a microscope slide

STEP EXPLANATION

Add a drop of water to the slide Create a seal between the slide and cover slip, stops sample drying out

Place a thin piece of the tissue to be viewed on the drop of water

The tissue needs to be thin to allow light to pas through it

Stain the tissue This allows structures in the tissue to be seen more easily

Place a cover slip gently on top of the tissue

This creates a seal between the tissue, slide and cover slip preventing bubbles which would obscure the image.

Magnification – The degree to which we make an image look larger than it actually is

4.1.2 Cell division

MITOSIS cell division for growth and repair of cells (produces clones).

1. Parent Cell – Chromosomes condense become visible

2. Chromosomes make identical copies of themselves (replicate).

3. The chromosomes line up along the centre of the cell

called the equator.

4. The chromosomes split and one set of chromosomes are

pulled to each end of the cell.

5. The cytoplasm splits and the cell membrane starts to form around each of the new cells

6. Two new daughter cells withidentical chromosomes to the

parent cell. The cells are diploid.

Genetic information is in the nucleus of cellsInside the nucleus are chromosomes made up of DNA –BODY CELLS have two sets of chromosomes (diploid) ,

SEX CELLS (gametes) have one set of chromosomes (haploid) in humans body cells 46 chromosomes (23 pairs), sex cells (sperm/egg) 23 single chromosomes.

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.• Rare species can be cloned to protect from extinction.• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

The cell cycle describes the stages which cells go through to divide. There are 3 stages: 1. Cell growth to increase the number of organelles such

as cytoplasm and mitochondria2. DNA replication, where the amount of DNA doubles3. Mitosis where the DNA and cell contents divide into 2.

• Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.

• Bacteria can be grown in a nutrient broth solution or as colonies on an• agar gel plate.

Microorganisms can be grown in the lab

• A culture medium (agar) used containing an energy source (carbohydrate) and minerals.

• Petri dishes and agar are sterilised before use to kill microorganisms.

• Inoculating loops used are sterilised by heating in a Bunsen flame

• The inoculating loop is used to transfer microorganisms from the sample to the agar plate

• At all times equipment is kept near a Bunsen flame to draw any airborne microorganisms into the flame to ensure there is no contamination

• Lid of the Petri dish should be sealed with two pieces tape to stop microorganisms getting in (must not be fully sealed so oxygen can get in) .

• In school petri dishes incubated at 25°C reduces risk of growth of pathogens that might be harmful to humans.

Culturing microorganisms – required practical

• Agar inoculated with BACTERIA.

• Paper discs containing antiseptics and antibiotics placed on bacteria using sterilised forceps

• Water DISK used as a CONTROL.

• Agar plate is sealed using two pieces of tape

• Agar is incubated for 24-48 hours

• If bacteria don’t grow around the disk then it is effective at killing bacteria.

• Area where bacteria don’t grow is called ZONE OF INHIBITION

4.1.3 Transport in cells

Diffusion is the spreading of the particles of a gas or liquid, resulting in a net movement of particles from a region where they are of a higher concentration to an area of lower concentration.

Substances may move into and out of cells using different processes.

Factors which increase the rate of diffusion:• A bigger difference in concentrations• A higher temperature• A bigger surface area (of the membrane).

A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs

of the organism.

In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by:• having a large surface area• having a membrane that is thin• having an efficient blood supply (in animals)• being ventilated (in animals).

Surface area = length x width= (4 x 4) x 2+ (4 x 2 ) x 4 = 64 cm2

Volume = length x width x height= 4 x 4 x 2 = 32 cm3

Surface area to volume ration = 64:32 (2:1)

Examples of diffusion

Part Function Adaptation

Lungs (alveoli)

To exchange oxygen and

carbon dioxide.

• Large surface area.• Moist lining.

• Very thin walls.• Good blood supply.

Smallintestine

(villi)

To pass digested food into the bloodstream.

• Single layer of surface cells.• Very good bloody supply.

Leaves in plants

Exchange carbondioxide and

oxygen.

• Flattened shape (increased area).• Air spaces in leaf.

• Guard cells to open and close stomata.

Gills in fish

To exchange oxygen and

carbon dioxide.

Gill filaments (big surface area).Lamellae on gill filaments.Lots of blood capillaries.

Large concentration gradient (due to direction of blood flow).

OSMOSIS is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of

lower water concentration.

• A partially permeable membrane has very small holes in it so only tiny molecules (e.g. water can pass through).

• The water molecules pass in both directions because they move randomly.

• Because there are more water molecules on one side than on the other, there is a steady net flow of water into the region with fewer water molecules (more concentration sugar solution).

• You can place potato cylinders in different sugar solutions (one should be pure water and one very concentrated and some in between).

• You measure the mass of the potato cylinder, place it in the sugar solution for 24 hours and then measure the mass after (must be dry).

• If the mass has increased – water has been taken in by osmosis.• If the mass has decreased – water has been given out by osmosis.

IV – concentration of sugar solution.DV – mass of potatoCV – volume of solution, temperature, time, type of sugar etc.

ACTIVE TRANSPORT - Active transport is the movement of a substance against a concentration gradient (from low to high), using energy from respiration.

Root hairs in plants take in minerals using active transport.

Active transport happens in the gut

Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration

of nutrients in the blood.This happens when diffusion cannot occur.

Type of solution

Description Effect on animal cell Effect on plant cells

Hypotonic Solution surrounding the cell contains less solute than inside the cell

Water from the solution surrounding the cell enters the cell. The mass of the cell increases. Eventually the cell bursts. This is called lysis.

Water from the solution surrounding the cell enters the cell. The mass of the cell increase. Eventually the cell becomes turgid as the cell wall supports the cell and prevents bursting

Isotonic Solution surrounding the cell has the same solute concentration as the solution inside the cell

No overall net movement in or out of the cell. This is the state the cell is found in normally.

No overall net movement in or out of the cell.

Hypertonic Solution surrounding the cell contains more solute than inside the cell

Water from cells leave to surrounding solution. The mass of the cell decreases. The cell shrivels. This is called crenation.

Water from cells leave to surrounding solution. The mass of the cell decreases. The cell shrivels and becomes flaccid and eventually becomes plasmolysed.