Cell Structure

Eukaryotic cells have a nucleus enclosing their DNA. Prokaryotic cells have no nucleus.

Animals, plants, fungi and single-celled organisms such as Amoeba.

A prokaryotic cell.

In a single loop lying free in the cytoplasm.

A small extra ring of DNA in a bacterial cell, often carrying genes such as antibiotic resistance.

It supports the cell and protects it. It is not made of cellulose.

Cell membrane, cytoplasm and ribosomes.

About 10 times: around 20 µm compared with around 2 µm.

One millionth, so \(1\ \mu\text{m} = 1 \times 10^{-6}\text{ m}\).

One billionth, so \(1\text{ nm} = 1 \times 10^{-9}\text{ m}\).

\(3 \times 10^{-5}\text{ m}\).

Two, because \(100 = 10^{2}\).

1000.

Thinking bacteria have no DNA. They do, but it is not enclosed in a nucleus.

What is the structure marked X in this bacterial cell?

A plasmid: a small extra ring of DNA that can carry genes such as antibiotic resistance.

It contains the genetic material (DNA) and controls the activities of the cell.

Most of the cell's chemical reactions.

It controls which substances pass into and out of the cell.

They are where aerobic respiration takes place, releasing energy for the cell.

They make proteins.

Cellulose.

It strengthens the cell and supports the plant.

The green pigment chlorophyll, which absorbs light for photosynthesis.

Cell sap, a solution of sugars and salts.

Cell wall, chloroplasts and a permanent vacuole.

Contraction needs a lot of energy, which mitochondria release in respiration.

Roots are underground where there is no light, so photosynthesis cannot happen.

No. They release energy from glucose in respiration. Energy cannot be made.

What is the structure marked X, and what does it do?

A mitochondrion. It is where aerobic respiration takes place, releasing energy for the cell.

Name the structure marked X, and say what it does.

A chloroplast. It contains chlorophyll, which absorbs light for photosynthesis.

Name the large structure marked X in this plant cell. What does it contain?

The permanent vacuole. It is filled with cell sap, a solution of sugars and salts.

Magnification = size of image ÷ size of real object.

Real size = image size ÷ magnification.

How clearly two points that are close together can be told apart.

The electron microscope.

It is large and expensive, and the specimen must be dead.

It is cheap and easy to use, and living cells can be viewed.

×400.

1000.

1000.

It makes the cell structures easier to see.

The lowest power one, which gives the widest view.

The coarse focus wheel finds it, then the fine focus wheel sharpens it.

To avoid trapping air bubbles.

Sharp pencil, clear single lines, no shading, labelled, with the magnification written.

Name part X of the microscope and say what it does.

The stage. It is the platform that holds the slide, kept in place by the clips.

Name part X of the microscope and say what it does.

The fine focus wheel. It makes small adjustments to give a sharp, clear image, after the coarse wheel has found it.

A cell with a structure that is suited to its particular job.

The process by which a cell changes to become specialised.

So it can swim to the egg.

They release the energy needed for swimming.

It contains enzymes that digest the outer layer of the egg so the sperm can get in.

It has a long axon, and a myelin sheath that insulates it.

They connect to many other nerve cells.

Special protein fibres that slide over each other, and many mitochondria for energy.

The long projection gives a large surface area to absorb water and minerals.

It speeds up the movement of water into the cell.

Water and mineral ions, from the roots up to the leaves.

The rings stop the hollow tube collapsing and make it strong.

Dissolved sugars to wherever they are needed.

The walls between phloem cells, with holes that let sugars flow through.

Their mitochondria supply the energy for moving sugars.

Plant cells. Most animal cells differentiate early.

Cell, tissue, organ, organism.

Name the part marked X on this sperm cell, and explain why it is there.

Mitochondria in the middle section. They release the energy from respiration that the tail needs for swimming.

Name the part marked X on this nerve cell and say what it does.

The myelin sheath. It is a fatty layer that insulates the axon and speeds up the impulse.

What is the structure marked X on this root hair cell, and how does it help?

The root hair. Its long, thin shape gives a large surface area for absorbing water and mineral ions from the soil.

By binary fission: a cell divides into two identical cells.

As often as once every 20 minutes, with enough nutrients and a suitable temperature.

In nutrient broth, or on agar gel in a Petri dish.

Methods used to stop unwanted microorganisms getting into a culture.

To kill any microorganisms already on them.

To kill microorganisms on it, so only the wanted bacteria are transferred.

To stop microorganisms from the air getting in.

So that oxygen can get in, which stops harmful anaerobic bacteria growing.

25 °C.

Higher temperatures make it more likely that harmful pathogens grow.

8 (three divisions: 2, 4, 8).

Divide the time by the mean division time.

The antibiotic or antiseptic has killed the bacteria or stopped them growing there.

The chemical is more effective.

\(A = \pi r^{2}\), where r is the radius (half the diameter).

To show that the paper itself does not stop the bacteria growing.

Which antibiotic is most effective here, and how can you tell?

Disc A. It has the biggest clear zone, so it killed or stopped the growth of the most bacteria.