B1 - Cell Biology

Question 1

Eukaryotic Cells

Answer 1

• Animals cells (contain nucleus, cytoplasm, cell membrane, mitochondria, ribosomes)
• Plant cells (contain nucleus, cytoplasm, chloroplasts, cell membrane, cell wall, permanent vacuole, mitochondria, ribosomes)

Question 2

Prokaryotic Cells

Answer 2

• Bacteria cells (contain free-flowing strand of DNA, cytoplasm, cell membrane, cell wall, flagella)

Question 3

Specialised Cells

Answer 3

When a cell undergoes differentiation: a process in which the cell develops new sub-cellular structures that allow it to carry out a specific role

Question 4

Sperm Cells

Answer 4

Function: to get the male DNA to the egg cell for successful reproduction
Adaptations: streamlined head and long tail to aid swimming, lots of mitochondria to supply energy for movement, acrosome that has digestive enzymes which break down the outer layers of the egg cell’s membrane

Question 5

Nerve Cells

Answer 5

Function: to transmit electrical signals around the body
Adaptations: long axon that enables impulses to be carried over long distance, lots of dendrites that connect to other nerve cells, many mitochondria in the nerve ending to supply energy to make neurotransmitters which allow the impulses to be passed from one cell to another

Question 6

Muscle Cells

Answer 6

Function: to contract quickly or squeeze and therefore trigger movement
Adaptations: contain special proteins that slide over each other to allow for contraction, contain lots of mitochondria to provide energy for cellular respiration, store glycogen that is used by mitochondria in respiration

Question 7

Root Hair Cells

Answer 7

Function: to absorb water and mineral ions from the soil
Adaptations: large surface area to allow for greater rate of diffusion of water, permanent vacuole to increase speed of osmosis from soil to cell, lots of mitochondria to provide energy for active transport

Question 8

Phloem Cells

Answer 8

Function: to transport products of photosynthesis around the plant
Adaptations: contain sieve plates that allow movement of substances from cell to cell, supplied with energy by the mitochondria of companion cells

Question 9

Xylem Cells

Answer 9

Function: to transport water and mineral ions from the roots to the shoots
Adaptations: cells are dead and become hollow tubes that join end to end so water and mineral ions can move through, lignin is desposited in spirals to help cells withstand the pressure the from the water movement

Question 10

Magnification

Answer 10

Magnification is how much bigger the image is than the actual specimen
Magnification = image size ÷ actual size
- centi (c) = x10^-2
- milli (m) = x10^-3
- micro (µ) = x10^-6
- nano (n) = x10^-9

Question 11

Diffusion

Answer 11

The spreading out of particles from an area of high concentration to an area of low concentration.
Examples of this include:
- gas exchange
- the movement and excretion of urea
The rate of diffusion is impacted by:
- concentration gradient
- temperature
- surface area of the membrane
- thickness of membrane

Question 12

Osmosis

Answer 12

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

Question 13

Active Transport

Answer 13

The movement of substances against the concentration gradient; this process requires energy from respiration

Question 14

Stem Cells

Answer 14

Cells which have the ability to differentiate
- there are two types in humans: adult and embryonic
- they can also be found in plants, in the meristem

Question 15

Uses of Stem Cells

Answer 15

Replacing faulty blood cells, making insulin producing cells, making nerve cells and growing crops with specific features, e.g. disease resistant

Question 16

Embryonic vs Adult Stem Cells

Answer 16

Embryonic stem cells:
- can turn into any kind of cell
- some argue its unethical as embryos are human life
Adult stem cells:
- can only turn into some types of cells
- procedure is always consensual

Question 17

Mitosis

Answer 17

1) DNA is replicated
2) DNA strands coil up into chromosomes
3) nuclear membrane breaks down and chromosomes line up along the centre of the cell
4) cell fibres attach to the chromosomes and pull them apart
5) membranes form around each set of chromosomes, making the nuclei of the new cells
6) cytoplasm divides and two new genetically identical daughter cells are formed

Question 18

Exchange in Plants

Answer 18

The surface of the leaf is flat to increase surface area for more gas exchange via diffusion (in = carbon dioxide, out = oxygen)
Oxygen and water vapour diffuse out the stomata; guard cells open and close the stomata, controlling water loss

Question 19

Exchange in Humans

Answer 19

Lungs: gas exchange occurs in the alveoli, which have a large surface area, moist lining, thin walls and a good blood supply
Small Intestine: villi (a single layer of cells with a good blood supply) increase the surface area to absorb more food

Question 20

Exchange in Fish

Answer 20

Water enters the fish through the mouth and goes out through the gills. The oxygen is transported from the water to the blood by diffusion, and carbon dioxide diffuses from the blood to the water.
Gills are the gas exchange surface in fish - each has gill filaments, which are covered in lamellae to increase the surface area and they have a thin surface layer and capillaries for good blood supply which helps with diffusion.

Question 21

Osmosis and Potato Practical

Answer 21

1) cut a potato into identical strips and get some beakers with different sugar solutions
2) measure the mass of the strips
3) leave them for the same amount of time, e.g. 24 hours
4) remove from solutions, dry with a paper towel and measure their masses again
- if its mass increased, water has been drawn in by osmosis
- if its mass decreased, water has been drawn out by osmosis

Question 22

Sub-cellular Structures

Answer 22

Nucleus: contains DNA coding for a particular
Cytoplasm: contains enzymes that speed up the rate of chemical reactions that occur there
Cell Membrane: controls what enters and leaves the cell
Mitochondria: where aerobic respiration occurs
Ribosomes: where protein synthesis occurs
Chloroplasts: where photosynthesis occurs
Permanent Vacuole: increases rigidity
Cell Wall: helps the cell maintain its shape and strengthens it

Question 23

Resolution

Answer 23

Resolution is the ability to distinguish between two points

Question 24

Microscopes

Answer 24

Light Microscope: cheap, portable and can use live specimen, but has a lower magnification and resolution
Electron Microscope: much higher magnification of up to 2,000,000x and much higher resolution, but is not portable, is expensive and can only use dead specimen

Question 25

Preparing Slides Practical

Answer 25

1) Peel of single layer of onion skin (the plant epidermis)
2) lay flat on clean microscope slide
3) add a drop of iodine
4) used a mounted needle to slowly lower the coverslip over the stain, making sure there are now air bubbles

Question 26

Culturing Microorganisms Practical

Answer 26

1) Clean desks and hands with an disinfectant/antibacterial spray
2) set up bunsen burner to sterilise environment
3) sterilise and use inoculating loop to transfer bacteria to agar jelly in a zig-zag motion
4) place the lid onto the agar plate and secure it with tape
5) leave for 2 days in 25°C