Cell Biology

Question 1

What are prokaryotic and eukaryotic cells?

Answer 1

Eukaryotic cells are complex and include all animal and plant cells.
Prokaryotic cells are single celled organisms eg. bacteria

Question 2

What are the structures of an animal cell and what is each function?

Answer 2

Nucleus - contains genetic material and controls cell activity
Mitochondria - where aerobic respiration takes place
Cytoplasm - gel-like and where chemical reactions take place
Cell Membrane - controls what goes in and out the cell
Ribosomes - where protein synthesis takes place

Question 3

What are the structures of a plant cell and what are the functions of each one?

Answer 3

Nucleus - contains genetic material and controls cell activity
Mitochondria - where aerobic respiration takes place
Cytoplasm - gel-like and where chemical reactions take place
Cell Membrane - controls what goes in and out the cell
Ribosomes - where protein synthesis takes place
Cell wall - supports and strengthens the cell and is made of cellulose
Permanent vacuole - contains cell sap to keep the cell turgid
Chloroplast - where photosynthesis takes place and contains chlorophyll to absorb light for photosynthesis

Question 4

What’s the structure of bacteria?

Answer 4

Bacteria don’t have a nucleus, chloroplasts or mitochondria but have a single circular strand of DNA, sometimes small rings of DNA called plasmids, cytoplasm, cell wall and a cell membrane.

Question 5

What’s the equation for magnification?

Answer 5

magnification = image size / real size

Question 6

What does a light microscope do?

Answer 6

It uses light and lenses to form an image and magnify it.
It lets us see individual cells and sub cellular structures.
It has a high resolution.

Question 7

What are the parts of a light microscope?

Answer 7

• Eyepiece
• High and low powered objective lens
• Coarse adjustment knob
• Fine adjustment knob
• Light
• Stage

Question 8

What does an electron microscope do?

Answer 8

It uses electrons to form an image.
It lets us see smaller things like the structure of mitochondria and tinier things like ribosomes.
It has a higher magnification than a light microscope.
It has a high resolution.

Question 9

How do you prepare a slide to see view onion cells?

Answer 9

• Add a drop of water to the middle of a clean slide.
• Cut an onion and separate into layers.
• Peel off the epidermal tissue with tweezers.
• Add a drop of iodine solution to highlight objects in a cell.
• Add a cover slip

Question 10

How do you use a light microscope?

Answer 10

• Clip the slide to the stage
• Select the lowest powered lens
• Use the coarse adjustment knob to move the stage just below the objective lens.
• Use the coarse adjustment knob to move the stage downwards until the image’s roughly in focus.
• Adjust the focus with the fine adjustment knob until it’s clear.

Question 11

What is differentiation?

Answer 11

The process of cells becoming specialised.

Question 12

What are specialised cells mainly used for in mature animals?

Answer 12

Repairing and replacing cells.

Question 13

How are sperm cells specialised for its function?

Answer 13

Its function is to get the male DNA to the female DNA.
It has a long tail and a streamlined head to swim to the egg.
It has mitochondria for energy.
It has enzymes to digest through the egg’s cell membrane.
It has a large nucleus which contains DNA to create offspring.

Question 14

How are nerve cells specialised for its function?

Answer 14

Its function is to carry electrical signals from one part of the body to another.
They have a long axen to carry the impulse.
Have nerve endings which release chemical messengers that cause impulses to carried in another nerve cell.
They have dendrites to connect to other nerve cells and form a network throughout the body.

Question 15

How are muscle cells specialised for its function?

Answer 15

Its function is to contact quickly.
It’s long so there’s space to contact.
It has lots of mitochondria to have gain energy for contraction.
Can store glycogen for respiration.

Question 16

How are root hair cells specialised for its function?

Answer 16

Its function is to absorb water and minerals.
It has a large surface area to increase the rate of absorption and a large vacuole to speed up osmosis.
It has lots of mitochondria to provide energy for active transport.

Question 17

How are phloem and xylem cells specialised for its function?

Answer 17

Xylem and phloem cells form to make xylem and phloem tubes, which transport substances like food and water around the plant.
The cells have to be long and joined end to end to form tubes.
Xylem cells are hollow (have no cell walls).
Xylem have lignin to strengthen the cell.
Phloem cells have few sub cellular structures so substances can easily flow through them.
They have sieve plates to easily allow dissolved food to move.
Has companion cells which have mitochondria for energy.

Question 18

What are undifferentiated cells called and what can they do?

HINT: divide

Answer 18

Stem cells and they divide to produce more undifferentiated cells which can differentiate into different types of cell.

Question 19

Where are stem cells found?

Answer 19

Early human embryos

Question 20

Where are adult stem cells found?

Answer 20

Bone marrow

Question 21

What can stem cells be used for?

Answer 21

Replacing faulty cells and curing diseases

Question 22

Reasons for and against stem cell research:

Answer 22

For:
• Curing patients that already exist are more important than embryos
• Embryos used are from abortions. 
Against:
• Human embryos are a potential life.

Question 23

Where are stem cells found in plants?

Answer 23

The meristems

Question 24

What are chromosomes?

Answer 24

Coiled up lengths of DNA molecules.

Question 25

How many pairs of chromosomes do humans have?

Answer 25

23

Question 26

What’s the cell cycle?

Answer 26

First, cell growth and DNA replication.
The cell grows, increase the amount of sub cellular structures and duplicates its DNA.

Mitosis:
The chromosomes line up in the centre of the cell and are pulled apart by cell fibres to different ends of the cell. Membranes form around each set of chromosomes (dividing the nucleus). Then the cell membrane and cytoplasm divides, forming two new identical daughter cells

Question 27

How do prokaryotic cells reproduce?

Answer 27

Binary fission:
The circular DNA strand and plasmids replicate.
The cell increases in size and the circular DNA strands move to opposite ends of the cell.
The cytoplasm and the cell membrane divides, making two new cells.
(Plasmids can vary in each cell)

Question 28

What’s a culture medium?

Answer 28

A place which contains the carbohydrates, minerals, proteins and vitamins needed to grow, e.g agar jelly.

Question 29

How do you prevent your culture (growing bacteria) from contamination?

Answer 29

• Sterilise Petri dishes and culture medium to kill unwanted microorganisms.
• Sterilise inoculating lip by passing it through a hot flame.
• The lid of the Petri dish should be taped on to stop microorganisms getting in the air.
• Store Petri dish upside down to stop drops of condensation falling on the agar surface

Question 30

How do you investigate the effect of antibiotics on bacterial growth?

Answer 30

• Soak paper discs in different toes of concentrations of antibiotics and place it on an agar plate with bacteria.
- Antibiotic-resistant bacteria will continue growing on the agar around the discs but non resistant bacteria dies.
- A clear area shows the bacteria has died (inhibition zone).
-Also, use a disc that hasn’t been soaked in the experiment to make sure any differences are an effect of the antibiotic.
• Leave the plate for 48 hours at 25 degrees.
- The more effective the antibiotic, the larger the inhibition zone.

Question 31

How do you find the area of an inhibition zone?

Answer 31

pi x radius squared

Question 32

What is diffusion?

Answer 32

The spreading out of particles from an area of higher concentration to an area of lower concentration.

Question 32

What can diffusion be used for?

Give an example.

Answer 32

Taking in substances and getting rid of waste products.

e.g urea diffuses into the blood plasma to be removed from the body by the kidneys.

Question 34

What factor can affect the rate of diffusion?

Answer 34

Temperature; the particles have more kinetic energy so they move faster.

Question 35

What can go through the partially permeable membrane?

Answer 35

Small things like amino acids, glucose, etc, but big molecules like starch and proteins can’t.

Question 36

What’s osmosis?

Answer 36

The movement of water molecules across a partially permeable membrane from a region of a high water concentration to a low water concentration.

Question 37

How to observe the effect of sugar solutions on potato/plant tissue?

Answer 37

• Cut a potato into identical cylinders.
• Get different beakers with different sugar solutions.
• Measure the mass of the potato pieces.
• Put it in the different breakers for the same time interval.
• Pat dry with a paper towel and measure the masses again.
• If the mass increases, the potato took in water but if the mass decreases, the potato released water.

Question 39

What’s active transport?

Answer 39

The movement of molecules into or out of a cell through the cell membrane, from an area of lower concentration to an area of higher concentration.
It requires energy.

Question 40

Why do root hair cells use active transport for mineral ions?

Answer 40

The concentration of mineral ions are higher in the root hair cells than in the soil so the root hair cells use active transport to take up the minerals from the soil.

Question 41

How does the SA:V ratio affect exchanging substances?

Answer 41

The larger the SA:V ratio, the easier exchanging substances are.

Question 42

How are exchange surfaces adapted to maximise excess?

Answer 42

Thin membrane for a short time to diffuse.
Large surface area so a lot more of a substance can diffuse at once.
(Animals) Many blood vessels to get things in and out of the blood quickly.

Question 43

How are alveoli in the lungs adapted to maximise diffusion?

Answer 43

• Large surface area
• A moist lining to dissolve gases
• Very thin walls
• God blood supply
(The lungs’ function is to transfer oxygen to the blood and remove carbon dioxide)

Question 44

How do villi help exchanging substances?

Answer 44

Villi provide a large surface area to maximise diffusion, a thin wall for a short diffusion time and has a good blood supply for quick absorption.

Question 45

How are leaves adapted for exchanging substances?

Answer 45

The stomata, controlled by the guard cells, lets carbon dioxide diffuse in the cell and oxygen and water vapour diffuse out.
The leaf’s flat shape and the air spaces in the cell increases surface area.

Question 46

How are gills in fish adapted for gas exchange?

Answer 46

Gill filaments create a large surface area for gas exchange
Lamellae, found on gill filaments, also have a large surface area.
They also have lots of capillaries to speed up diffusion, a thin surface layer to minimise diffusion distance.
Water and blood flow in opposite directions to maintain a large concentration gradient.

Question 47

How is active transport used in the body?

Answer 47

When there’s a lower concentration of glucose and amino acids in the gut than the blood so active transport takes place to allow nutrients to be taken from the blood.