B2.1

Question 1

What is Diffusion?

• What does it mean by being a passive process?

Answer 1

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient (until the conc gradient is 0)

2) this means energy is not transferred during diffusion- it happens due to ordinary motion of particles in air.

Question 2

Where does diffusion take place?

Answer 2

Diffusion takes place in our body in our cells that need glucose and oxygen. Diffusion also happens out for waste products formed, such as Co2

Question 3

How does SA: V ratio help diffusion and where?

Answer 3

1) surface area to volume ratio
- By increasing to SA:V ratio, the rate of diffusion increase (remember do this by smaller organism) this happens in small intestine wall, which is highly folded increasing the surface area touching the oxygen in the same volume, increasing the diffusion if molecules produced in digestion such as glucose and amino acids which is very useful.

Question 4

How decrease distance help diffusion?

Answer 4

By decreasing the distance particles need to move, the rate of diffusion increase.

Such as in blood capillaries which are ONE CELL THICK, it takes less time for particles to diffuse across a shorter distance easy.

Question 5

How does concentration gradient affect the rate of diffusion?

Answer 5

Increase the concentration gradient leads to a higher net movement of particles and more diffusion.

For example as plants use co2 for photosynthesis, the concentration of co2 decreases, which increases the concentration gradient - leading to a greater net movement of particles.

(Similarly in animals at exchange surfaces you need a good blood supply so concentration gradient is always kept low)

Question 6

What are difficulties of diffusion with unicellular organisms vs complex multi cellular ones?

Answer 6

What osmosis?

Question 7

What is osmosis?

Answer 7

Osmosis is the net movement of water molecules from an area of high WATER POTENTIAL to an area of low WATER POTENTIAL down a concentration gradient through a partially permeable membrane. (Such as a CELL MEMBRANE)

(Still a type of diffusion but just for water molecules)

Question 8

What happens to cells in plants with osmosis

Answer 8

1) if surroundings are less concentrated (meaning more water potential) then cells, then water will move in to the cell, causing it to expand and increases tugor pressure. This means it becomes TUEHID/ FIRM.

(Plants take water in from high water potential soil until they have a decent tugor pressure, or else they droop. They still maintain shape thanks to inelastic cell wall though)

2) same concentration nothing happens
3) if surroundings are more concentrated ( meaning they have less water potential) then water will move out of the cell. This causes a loss of turgor pressure and causes the cell to become FLACCID. Eventually cell contents collapse away from the cell wall- this cell is now under PLASMOLYSIS.

Question 9

What happens to human cells with osmosis?

Answer 9

1) if surroundings are less concentrated, then water moves into cells. This causes cell to expand swell and potentially burst = LYSIS
2) same then same as no net movement of water
3) if surroundings are more concentrated, then water moves out of cell. This causes the cell to become CRENATED (it crinkles).

Question 10

Summary of what happens to plant and animal cell

Answer 10

Plant
Water in = turgid firm
Water out = flaccid. Eventually contents collapse- >plasmolysis

Animal
Water in = lysis and may burst
Water out= crenated (crinkles)

Question 11

What is active transport and what does it use (2 things)

Answer 11

Active transport is the movement of particles from an area of low concentration to an area of high concentration against a concentration gradient , using carrier proteins to do so.
- going against the concentration gradient it requires ATP too.

Question 12

Why do cells that carry out active transport need mitochondria?
- what does this tell you about the rate of active transport.

Answer 12

Cells that carry out active transport contain more levels of mitochondria as ATP is required for the carrier proteins to rotate. This shows that rate of active is proportional and dependent to the rate of respiration

Question 13

What are carrier proteins?

Answer 13

• proteins that SPAN ACROSS THE WIDTH OF THE CELL MEMBRANE and are found in the cell membrane
• they transport molecules in active transport in and out of membrane. They bind to the molecule, rotate or change shape and then release. However this requires energy .

Question 14

Examples in plants and human small intestine

Answer 14

1) plants use it to transport nitrates and minerals from the soil to them, to make proteins for example. There is always going to be or normally a lower concentration of nitrate particles in the soil, therefore active transport instead of diffusion must be used. Root hair cells use active to transport them into the cell.
2) the glucose that just digests in small intestine actively transport into vili, as it would be inefficient to wait for diffusion as we would starve.

Question 15

No mitosis: what is mitosis and what is it used for (3 things). What does it produce

Answer 15

Mitosis is the process by which cells divide, mitosis is used for REPAIR damaged TISSUE, enable to organism to increase in size, and replace worn out cells. Also finally for asexual reproduction for other organisms

( can’t say repair cells- they would just get replaced)

• Mitosis produces two genetically identical daughter cells from 1 parent cell.

Question 16

What are the 4 stages of mitosis which is known as the cell cycle?

Answer 16

1) DNA Replication
2) movement of chromosomes
3) cytokinesis
4) growth of daughter cells

Question 17

How does DNA replication work?

Answer 17

) Double Helix molecule unzips to expose both strands

2) free nucleotides in the nucleus line up against the strand, based on complementary base pairing.
3) DNA base pairs are made, and when all of them are done

= two new genetically identical molecules of DNA. They zip back together.

Question 18

How does movement of chromosomes work

Answer 18

This forms bulk of mitosis ,PMAT

1) Chromosomes all line up in the centre of the cell
2) the chromosomes are pulled apart two opposite ends f the cell by spindle fibres.
3) two new nuclei form around each set of chromosomes which now contain all the genetic information for the cell.

Then cytokinesis takes place

Question 19

How does cytokinesis work?

Answer 19

This is last stage o

1) the cell membrane then pinches inwards on the two cells, separating them, and then they split off the parent cell to become two genetically identical daughter cells.

Question 20

Finally what happens in growth of daughter cells

Answer 20

Here the daughter cells then independently gore . Finally the cycle repeats as when the time comes the whole process will happen again…

Question 21

How often does mitosis take place in parts of the body? Why does it vary?

Answer 21

Approximately 300 million body cells die and are replaced every minute. However mitosis happens all the time in places like the skin, but rarely in places like nerves which don’t need to be replaced all the time…

Times of cell cycles vary in different tissues because of different replacement rates- some replace there’s Often, others don’t.

Question 22

What does it mean for a cell to differentiate during development ?

Answer 22

It means the process by which a cell changes to become SPECIALISED for a specific job .

This involves changing structures or producing sub cellular structures to be more adapted for a job. This makes the entire organism more efficient.

Cells can be so specialised they only perform one function in the body- such as red blood cells

Question 23

So what is a stem cell and what are they used for?

Answer 23

Stem cells are undifferentiated cells in the human body that divide by mitosis and can differentiate into many types of cells - forming types of tissues and organs.

• Split into adult stem cells and embryonic stem cells.
• they are used by the body DURING DEVELOPMENT, growth and repair.

Question 24

Embryonic stem cells

Where found
What can they do
What do they do

What important for

Answer 24

• Found in Embryos (which is formed after zygot divides)
• All cells are totipotent= embryonic stem cells can differentiate into any type of cells.
• divide by mitosis and important in development of a human as they produce all the different cells needed

Question 25

Adult stem

Where found
What can they do
What do they do

What important for

Answer 25

• Are found in various different areas : brain, bone marrow, skin and liver (remember liver can regrow up to like 25%)
• They are only able to differentiate into some types of cells, but not all like embryonic- this makes them multipotent.

: for example, blood stem cells found in bone marrow can differentiate into red blood cells, white blood cells and platelets, but not like muscle cells. Or also skin cells too…

They are important for growth but mostly repair, as they remain in an undividing state for years until needed due to injury or disease.

Question 26

What about stem cells (meristem tissue) in plants, what makes them different to mammals , and why can’t differentiated cells divide?

Answer 26

Plant unlike mammals can CONTINUE to differentiate throughout their life and din’t stop growing. Like embryonic but extended forever .

However once cells have become differentiated they can no longer divide because if rigid and thick cell walls, but MERISTEM cells can always divide and differentiate by mitosis.

Question 27

Arguments for and against embroidery stem cell treatment

Answer 27

For

• as stem cells are multipotent there’s a limit to what they can do to help. However embryonic can differentiate into anything which means they ca help for things like paralysis , as nerve cells are only made once.
• they would be destroyed anyways as they come from IVF, might as well use them for something
• thereperitic cloning can be used (which overcomes rejection of foreign cells and need for i uni suppressants)

Against
- all embryos have intrinsic right to live
- unable to give rejection in consent
Religious
- taken from a 4-5 day old embryo

Question 28

Where are meristem cells found, and what do they contain.

Answer 28

• contains very thin wall, small vacuoles but no chloroplasts
• Found in Root tips, shoot tips and buds

Question 29

How are sperm cells specialised?

Answer 29

Specialised for transfer genetic material to egg.

• Has flagellum which propels sperm to the ovum by whipping side to side. Need to swim
• Has an across me- this is a store of DIGESTIVE enzymes which are needed to break down the outer layers of the ovum to allow the sperm to successfully transfer the genetic material.
• contains a lot of mitochondria- respiration needs to be happened at all times to get ATP required to move the speem in flagella

Question 30

How are fat cells specialised.

Answer 30

Adapted to store fat, which can be used as a store for energy but also insulation and protective layer for vital organ like heart. Too much bad off

• Has A SMALL LAYER OF CYTOPLASM surrounding a FAT RESERVOIR. This can expand to 1000 times its original size as it fills with fat, therefore a small layer of cytoplasm is needed.

Question 31

How are red blood cells specialised to perform its function

Answer 31

Red blood cells are specialistsisdd to transport oxygen around the body.

• PACKED with haemoglobin. This binds with oxygen to form oxyhemoglobin, which is bright red, and is how oxygen is carried. The more haemoglobin the more oxygen.
• HAS NO NUCLEUS: this means there is more space to fit in more haemoglobin and thus more oxygen
• BICONCAVE DISK: Red blood cell is essentially pushed in on both sides, which increase the SA:V ratio, which increases rate if diffusion oF oxygen into cell and carbon dioxide Exit, which in turn means more respiration can happen.

Question 32

How are ciliates cells specialised (they have goblet too)

Answer 32

Dilated cells are specialised to trap bacteria when breathing

• IN BETWEEN CILAITED CELLS ARE GOBLET CELLS: this produces sticky mucus which traps dirt and bacteria.
• Cillia which are tiny hairs then SWEEP the mucus away from lungs and into throat, where after swallow bacteria is killed in stomach.

Question 33

How are Palisade cells (ordinary photosynthesis ones) specialised

Answer 33

Palisade cells are specialised for carrying out photosynthesis.

• PACKED FULL OF CHLOROPLASTs: this means they can carry out more photosynthesis.
• REGULAR SHAPE : this allows a lot of the cells to be closely packed together near the top of the leaf, for maximum absorption if sunlight and more photosynthesis

Question 34

How are root hair cells specialised?

Answer 34

Millions of microprocessors hairs increase surface area for osmosis and mineral ions via active transport
, as molecules can only cross cells right next so higher surface area gives this