Cell Biology

Question 1

What does a nucleus do?

Answer 1

It contains genetic material and controls the activities of the cell

Question 2

What does cytoplasm do?

Answer 2

It’s a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions

Question 3

What does a cell membrane do?

Answer 3

It holds the cell together and controls what goes in and out

Question 4

What do mitochondria do?

Answer 4

These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work

Question 5

What do ribosomes do?

Answer 5

This is where protein synthesis takes place - where proteins are made in the cell

Question 6

What do cell walls do?

Answer 6

They are made of cellulose and they support and strengthen the cell

Question 7

What does a vacuole do?

Answer 7

It contains cell sap and helps maintain the shape of the cell

Question 8

What do chloroplasts do?

Answer 8

This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis

Question 9

What do bacterial cells contain?

Answer 9

Cytoplasm, cell membrane, cell wall, flagella, ribosomes, mitochondria, slime capsule, plasmids (small rings of DNA) and a single circular strand of DNA that floats freely in the cytoplasm

Question 10

What do bacterial cells NOT contain?

Answer 10

A nucleus

Question 11

What is the equation for magnification?

Answer 11

Image size divided by actual size

Question 12

What is differentiation?

Answer 12

The process by which a cell changes to become specialised for its job

Question 13

What are undifferentiated cells called?

Answer 13

Stem cells

Question 14

What are sperm cells specialised for and how are they specialised?

Answer 14

Reproduction - they transport the male DNA to the female DNA
-It has a flagella and a streamlined head to help it swim towards the egg
-There are lots of mitochondria in the cell to provide the energy needed
-It carries enzymes in its head to help digest through the egg cell membranes

Question 15

What are nerve cells specialised for and how are they specialised?

Answer 15

Rapid signalling - they carry electrical signals from one part of the body to another
-They are long to cover more distance
-They have branched connections at their ends to connect to other nerve cells and form a network throughout the body

Question 16

What are muscle cells specialised for and how are they specialised?

Answer 16

Contraction - they need to contract quickly
-They are long so they have space to contract
-They contain lots of mitochondria to generate the energy needed for contraction

Question 17

What are root hair cells specialised for and how are they specialised?

Answer 17

Absorbing water and minerals
-They are cells on the surface of plant roots which grow into long hairs that stick out into the soil
-They have a large surface area for absorbing water and mineral ions from the soil

Question 18

What are chromosomes?

Answer 18

Coiled up lengths of DNA molecules that are found in the nuclei

Question 19

What do multicellular organisms use mitosis for?

Answer 19

To grow or replace cells that have been damaged

Question 20

What are stem cells?

Answer 20

They are undifferentiated cells that divide to produce lots more undifferentiated cells. They then differentiate into different types of cell

Question 21

Where are stem cells found?

Answer 21

In early human embryos or the bone marrow of adults

Question 22

What do embryonic stem cells do?

Answer 22

1) Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries
2) Used to replace faulty blood cells

Question 23

What is diffusion?

Answer 23

Diffusion is the movement of particles from an area of high concentration to an area of low concentration

Question 24

Name the substances that can diffuse through cell membranes

Answer 24

Glucose, oxygen and amino acids

Question 25

Name two substances that can’t diffuse through cell membranes

Answer 25

Protein and starch

Question 26

What is osmosis?

Answer 26

Osmosis is the passive movement of water molecules through a partially permeable cell membrane from an area of high water concentration to an area of low water concentration

Question 27

What are the two main differences between active transport and diffusion?

Answer 27

Active transport uses energy whereas diffusion doesn’t. Active transport goes against the concentration gradient whereas diffusion goes along it

Question 28

Adaptations of Exchange Surfaces

Answer 28

1) Large surface area - lots of substances can diffuse at once
2) Lots of blood vessels - to get stuff into and out of the blood quickly
3) Thin membrane - short distance for substances to diffuse
4) Often ventilated - air moves in & out

Question 29

Give two ways that the villi in the small intestine are adapted for absorbing digested food

Answer 29

1) A single layer of surface cells
2) A very good blood supply to assist quick absorption

Question 30

Explain how the leaves are adapted to maximise the amount of carbon dioxide that gets into their cells

Answer 30

1) The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through
2) The leaf has a flattened shape which increases the area of its exchange surface therefore it’s more effective
3) The walls of the cells inside the leaf act as another exchange surface
4) The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells

Question 31

What affects the rate of diffusion?

Answer 31

Concentration gradient - the steeper the gradient, the faster the rate
Temperature - the higher the temperature, the faster the rate (the particles have more energy thus move around faster)
Surface area - the larger it is, the faster the rate
Diffusion distance - the shorter the distance, the faster the rate

Question 32

Examples of active transport

Answer 32

Plants = Root hairs absorb minerals and water. Each branch of a root will be covered in tiny hairs, therefore increasing the surface area for the absorption of minerals and water. The concentration of minerals is usually higher in the root hair cells than in the soil around them, therefore they can’t use diffusion for this process.
Animals = Glucose is taken in from the gut and from kidney tubules.

Question 33

How are alveoli in the lungs specialised to maximise the diffusion of oxygen and carbon dioxide?

Answer 33

-an enormous surface area
-a moist lining for dissolving gases
-very thin walls
-a good blood supply

Question 34

How do fish respire?

Answer 34

-Water enters the fish through the mouth and passes out through the gills
-During this process, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water

Question 35

How are fish adapted for gas exchange?

Answer 35

-Each gill is made up of lots of gill filaments which create a large surface area for the exchange of gases
-Gill filaments are covered in lamellae which increase the surface even more
-The lamellae have lots of blood capillaries to speed up diffusion
-The lamellae have a thin surface layer of cells to minimise the diffusion distance
-Blood flows through the lamellae one way and water flows over in the opposite direction which maintains a higher concentration gradient between the blood and the water
-The concentration of oxygen in the water is always higher than that in the blood to maximise the amount of oxygen diffusion from the water into the blood

Question 36

Microscopy Practical - Preparing the Slide

Answer 36

1) Add a drop of water to the middle of a clean slide
2) Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers
3) Using the tweezers, place the epidermal tissue into the water on the slide
4) Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them
5) Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there’ll obstruct your view

Question 37

Microscopy Practical - Using a Light Microscope

Answer 37

1) Clip the slide you’ve prepared onto the stage
2) Select the lowest-powered objective lens
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 the image is roughly in focus
5) Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide

Question 38

Microscopy Practical - Drawing Observations

Answer 38

1) Draw what you see under the microscope using a pencil with a sharp point
2) Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines
3) Your drawing should not include any colouring or shading
4) If you are drawing cells, the subcellular structures should be drawn in proportion
5) Include a title & write down the magnification that it was observed under
6) Label the important features of your drawing using straight, uncrossed lines

Question 39

What happens during binary fission?

Answer 39

1) The circular DNA & plasmid(s) replicate
2) The cell gets bigger & the circular DNA strands move to opposite poles of the cell
3) The cytoplasm begins to divide & new cell walls begin to form
4) The cytoplasm divides & two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)

Question 40

What is binary fission?

Answer 40

A type of simple cell division used by prokaryotic cells to reproduce & split into two

Question 41

What conditions do bacteria need to divide?

Answer 41

1) Warm environment
2) Lots of nutrients

Question 42

What is the mean division time?

Answer 42

The average amount of time it takes for one bacterial cell to divide into two

Question 43

How do you make an agar plate?

Answer 43

Hot agar jelly is poured into shallow Petri dishes. When the jelly’s cooled & set, inoculating loops can be used to transfer the microorganisms to the culture medium. Alternatively, a sterile dropping pipette & spreader can be used to get an even covering of bacteria. The microorganisms then multiply

Question 44

Investigating the Effect of Antibiotics on Bacterial Growth - Method

Answer 44

1) Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between the discs
2) The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria that aren’t affected by the antibiotic will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone
3) Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone
4) Leave the plate for 48 hours at 25°C
5) The more effective the antibiotic is, the large the inhibition zone will be

Question 45

Avoiding Contamination

Answer 45

1) The Petri dishes & culture medium must be sterilised before use (heating to a high temperature) to kill any unwanted microorganisms
2) If an inoculating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame
3) After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it
4) The Petri dish should be stored upside down - stops drops of condensation falling onto the agar surface

Question 46

Investigating the Effect of Sugar Solutions on Plant Tissue - Method

Answer 46

1) Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution
2) Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours
3) Take them out, dry them with a paper towel & measure their masses again
4) If the cylinders have drawn in water by osmosis, they’ll have increased in mass. If water has been drawn out, they’ll have decreased in mass
5) The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same

Question 47

Possible Errors of the Potato Chip Experiment

Answer 47

1) Some potato cylinders were not fully dried
2) Water evaporated from the beakers
3) The potato chips weren’t identical sizes
4) The volumes of water weren’t identical

Question 48

Types of eukaryotic cells

Answer 48

Animal cells

Question 49

What are light microscopes?

Answer 49

They use light & lenses to form an image of a specimen & magnify it

Question 50

What are electron microscopes?

Answer 50

They use electrons to form an image

Question 51

Disadvantages of Stem Cells

Answer 51

1) Stem cells grown in the lab may become contaminated with a virus - this will be passed onto the patient & make them sicker
2) Some people think that human embryos shouldn’t be used for experiments - each one is a potential human life
3) Scientists should focus more on finding & developing other sources of stem cells