GCSE AQA Biology B1

What is a eukaryotic cell?

A cell that has its genetic material enclosed in a nucleus

What are two examples of eukaryotes?

Animal cells and plant cells

What is a prokaryotic cell?

A cell where the genetic material is not enclosed in a nucleus

Give an example of a prokaryote

A bacterial cell

Compare the size of prokaryotes and eukaryotes

Prokaryotes are much smaller than eukaryotes

What is a plasmid?

A small loop of extra DNA found in prokaryotes

Where is the genetic material found in a prokaryote?

As a single loop of DNA floating freely in the cytoplasm

Name three sub-cellular structures found in both eukaryotic and prokaryotic cells

Cell membrane, cytoplasm and ribosomes

What is the function of the nucleus?

Contains genetic material and controls the activities of the cell

What is the function of the cytoplasm?

A gel-like substance where most chemical reactions take place

What is the function of the cell membrane?

Controls the passage of substances in and out of the cell

What is the function of mitochondria?

The site of aerobic respiration where energy is released for the cell

What is the function of ribosomes?

The site of protein synthesis

Name three structures found in plant cells but not animal cells

Chloroplasts, permanent vacuole and cell wall

What is the function of chloroplasts?

The site of photosynthesis where light energy is absorbed to make glucose

What is the function of chlorophyll?

A green pigment in chloroplasts that absorbs light for photosynthesis

What is the function of the permanent vacuole?

Contains cell sap to keep the plant cell turgid. Cell sap is made of dissolved dissolved sugars, mineral salts, and amino acids.

What is the function of the plant cell wall?

Strengthens and supports the cell

What is the plant cell wall made of?

Cellulose

What is cell specialisation?

When a cell differentiates to acquire specific structures that allow it to carry out a certain function

What is the function of a sperm cell?

To carry the male DNA to the female DNA in the egg for reproduction

How is the sperm cell tail adapted for its function?

It is long and streamlined to help the sperm swim to the egg

Why do sperm cells contain lots of mitochondria?

To transfer the energy needed for the tail to swim

What is the function of the acrosome in a sperm cell?

Contains digestive enzymes to penetrate the outer layer of the egg cell

Why does the sperm cell nucleus only contain half the normal amount of genetic material?

So it can fuse with the egg cell nucleus to form a diploid zygote

What is the function of a nerve cell?

To transmit electrical impulses rapidly around the body

How is the axon adapted for its function in a nerve cell?

It is very long to carry electrical impulses over large distances

What is the function of the myelin sheath on a nerve cell?

It insulates the axon and speeds up the transmission of electrical impulses

What is the function of dendrites on a nerve cell?

To form connections with many other nerve cells

What are synapses?

Junctions between nerve cells where chemicals are released to pass the impulse to the next cell

What is the function of a muscle cell?

To contract and cause movement

How do protein fibres help a muscle cell function?

They can slide over each other to allow the cell to contract and shorten

Why do muscle cells contain lots of mitochondria?

To release lots of energy for continuous contraction

What is the function of a root hair cell?

To absorb water and mineral ions from the soil

How is a root hair cell adapted for absorption?

It has a long hair-like extension that greatly increases the surface area

Why do root hair cells contain many mitochondria?

To release energy for the active transport of mineral ions from the soil

Why do root hair cells lack chloroplasts?

They are located underground where there is no light for photosynthesis

What is the function of xylem cells?

To transport water and dissolved mineral ions from the roots to the leaves

What substance strengthens the walls of xylem cells?

Lignin

Why are xylem cells dead and hollow?

To form a continuous tube that allows water to flow easily without resistance

What is the function of phloem cells?

To transport dissolved sugars up and down the plant

What are sieve plates in phloem cells?

Pores in the end walls that allow cell sap to flow freely between cells

Why do phloem cells have companion cells?

Phloem vessel cells lack many organelles so companion cells provide energy for transport

When do most types of animal cells differentiate?

At an early stage of development

When do most types of plant cells differentiate?

Plant cells retain the ability to differentiate throughout life

What is the main purpose of cell division in mature animals?

Repair and replacement of cells

What is a microscope?

An instrument used to view objects that are too small to be seen with the naked eye

What type of radiation does a light microscope use?

Visible light

What type of radiation does an electron microscope use?

A beam of electrons

Give an advantage of a light microscope

They are cheap, portable and can view living specimens

Give a disadvantage of a light microscope

They have a lower magnification and lower resolving power

Give two advantages of an electron microscope

They have a much higher magnification and higher resolving power

Give a disadvantage of an electron microscope

They are very expensive, large and can only view dead specimens in a vacuum

What is meant by magnification?

How many times larger the image is compared to the real object

What is meant by resolution or resolving power?

The ability to distinguish between two separate points that are very close together

State the equation for calculating magnification

Magnification = Image size / Real size

How many micrometres are in one millimetre?

1000

How many nanometres are in one micrometre?

1000

How do bacteria multiply?

By simple cell division called binary fission

How often can bacteria carry out binary fission under optimal conditions?

Once every 20 minutes

State the equation used to calculate the number of bacteria in a population

Number of bacteria = starting number x 2^number of divisions

What is a nutrient broth solution?

A liquid medium containing nutrients required for bacterial growth

What is an agar gel plate?

A solid medium in a petri dish that bacteria can grow on to form visible colonies

Why must petri dishes and culture media be sterilised before use?

To kill any unwanted microorganisms and prevent contamination

How do you sterilise an inoculating loop?

Pass it through a hot, roaring Bunsen burner flame until it glows red hot

Why is the lid of the petri dish secured with adhesive tape?

To prevent microorganisms from the air entering and contaminating the culture

Why should the petri dish not be completely sealed tightly with tape?

To allow oxygen in to prevent the growth of harmful anaerobic bacteria

Why are petri dishes stored upside down during incubation?

To stop drops of condensation falling onto the agar surface and disrupting the colonies

What temperature should bacterial cultures be incubated at in school laboratories?

25 degrees Celsius

Why are schools restricted to incubating cultures at 25 degrees Celsius?

To reduce the risk of growing dangerous pathogens that thrive at human body temperature

What is the zone of inhibition?

A clear area around a paper disc where bacteria have been killed or cannot grow

How do you determine the effectiveness of an antibiotic on an agar plate?

Measure the diameter of the zone of inhibition and calculate its area using pi x r^2

What does a larger zone of inhibition indicate?

That the antibiotic or antiseptic is more effective at killing the bacteria

Where are chromosomes found in a eukaryotic cell?

In the nucleus

What are chromosomes made of?

Long molecules of tightly coiled DNA

How are chromosomes normally arranged in body cells?

In pairs

How many pairs of chromosomes are in a normal human body cell?

23 pairs

What is a gene?

A small section of DNA on a chromosome that codes for a specific sequence of amino acids to make a protein

What is the cell cycle?

A series of stages that a cell goes through in order to divide

What happens during the first stage of the cell cycle?

The cell grows, increases the number of sub-cellular structures and replicates its DNA

What is mitosis?

The second stage of the cell cycle where the nucleus divides

Describe what happens to chromosomes during mitosis

One set of chromosomes is pulled to each end of the cell and the nucleus divides

What happens in the final stage of the cell cycle?

The cytoplasm and cell membrane divide to form two identical daughter cells

Why is mitosis important for multicellular organisms?

For growth, development and replacing damaged cells

What is a stem cell?

An undifferentiated cell capable of giving rise to more cells of the same type and differentiating into other cell types

Where are stem cells found in human embryos?

In the early embryo formed from a fertilised egg

What is the function of embryonic stem cells?

They can differentiate into any type of human cell

Where are adult stem cells found in humans?

In the bone marrow

What is the limitation of adult stem cells?

They can only differentiate into a limited number of cell types such as blood cells

What is therapeutic cloning?

Producing an embryo with the same genes as the patient so the stem cells are not rejected by the patient's body

Give a medical condition that could be treated using stem cells

Diabetes or paralysis

What is a risk of using stem cells in medicine?

They could be infected with viruses which are then transferred to the patient

What is a major ethical objection to using embryonic stem cells?

Some people believe it destroys a potential human life

Where are stem cells found in plants?

In the meristem tissue located at the tips of roots and shoots

What is a key feature of meristem tissue in plants?

It can differentiate into any type of plant cell throughout the life of the plant

Give a commercial advantage of using plant meristem stem cells

Rare plant species can be cloned quickly and cheaply to protect them from extinction

How can crop plants benefit from meristem cloning?

Large numbers of identical crop plants with special features like disease resistance can be produced

What is diffusion?

The net movement of particles from an area of higher concentration to an area of lower concentration

Is diffusion an active or passive process?

Passive because it does not require energy from respiration

Give two examples of substances transported into and out of cells by diffusion

Oxygen and carbon dioxide in gas exchange, and the waste product urea leaving cells