Biology Stupid Questions Part 4

Question 1

Explain why single celled organisms such as Amoeba and Paramecium can gain enough oxygen for aerobic respiration through simple diffusion across there cell surface membranes

Answer 1

single celled organisms can gain enough energy from oxygen through simple diffusion across there cell membranes as they are small therefore they do not need that much energy to function. The diffusion distance is short this means that diffusion along can supply the cell with all the oxygen it needs as the cell is close to the environment. furthermore it has a large surface area to volume ratio therefore the diffusion of oxygen can happen in many places at once.o

Question 2

How would you expect the direction of net diffusion of CARBON DIOXIDE in and out of a palisade mesophyll to differ
A - at noon on a sunny day compared with
B - at midnight
explain your answer

Answer 2

When it is noon on a sunny day the net diffusion of carbon dioxide would be inwards to the plant and it will enter the palisade mesophyll, this is because the stomata will be open for photosynthesis due to the light and warm temperatures therefore the carbon dioxide will travel from a high concentration outside the mesophyll cell to a low concentration inside the cell and down the concentration gradient.
Whereas at midnight there is no light therefore the plant cannot photosynthesises this means that the stomata will be closed and the net diffusion of carbon dioxide will be out of the plant as the cells will still be respiring and producing carbon dioxide even if the stomata are closed. The carbon dioxide goes from a high concentration to a low concentration down the concentration gradient

Question 3

How would you expect the direction of net diffusion of OXYGEN in and out of a palisade mesophyll to differ
A - at noon on a sunny day compared with
B - at midnight
explain your answer

Answer 3

At noon on a sunny day the net diffusion of oxygen would be out of the palisade mesophyll this is because the plant will be photosynthesising and the stomata will be open, therefore the product of photosynthesis is oxygen so there will be a high concentration of oxygen in the mesophyll and a low concentration outside the plant so there will be net outflow
at midnight, there will be net inflow of oxygen into the palisade mesophyll this is because the plant is using the oxygen for respiration and not photosynthesis and to release energy therefore as oxygen is a reactant it is taken into the plant from a high concentration outside to a low concentration inside and down the concentration gradient

Question 4

Explain why glucose and amino acids pass into or out of cells by facilitated diffusion

Answer 4

Glucose and amino acids have polarity and are insoluble in the lipid therefore they cannot interact with the hydrophobic tails in the phospholipid bilayer therefore they have to diffuse through protein channels and carrier proteins, these are hydrophilic so the amino acids and glucose can interact with the water molecules and are soluble within the water. moreover glucose is too big to diffuse through the water filled channel so instead go through the carrier proteins, this is facilitated diffusion

Question 5

when molecules diffuse they use their kinetic energy, explain why such diffusion is referred to as passive

Answer 5

all molecules have kinetic energy, but diffusion is passive as the molecules do not move against the concentration gradient so no energy is needed for the molecules to move, diffusion also does not use ATP so therefore is passive

Question 6

List 5 factors that affect the rate of diffusion and explain how each alters the rate of diffusion

Answer 6

• Temperature - as temperature increases more molecules have higher kinetic energy so rate of diffusion increases as there are more frequent collsions so molecules are more likely to travel in the correct direction
• Diffusion distance - the thicker the membrane the slower the diffusion rate as the molecules have to go a longer distance
• surface area - across a larger surface area more diffusion can take place this would increase the rate of diffusion - specialised cells for absorption have microvilli these increase the surface area
• size of diffusing molecules - small molecules diffuse more quickly than larger molecules
• concentration gradient - the steeper the concentration gradient the faster the diffusion to the side with fewer molecules

Question 7

if plant cells are placed in concentrated sucrose solution then they become plasmolysed what is in the space between the cellulose cell wall and the cell surface membrane

Answer 7

sucrose solution

Question 8

how will the factors of diffusion effect the rate of osmosis

Answer 8

temperature - increases the kinetic energy of the molecules therefore more frequent collisions and water molecules are likely to travel down the concentration gradient increasing the rate of osmosis
diffusion distance -short diffusion distance faster rate of osmosis
surface area - larger surface area faster rate of osmosis
size of diffusing molecules - water molecules are the same size therefore this would not matter
concentration gradient - steeper concentration gradient faster rate of osmosis

Question 9

why does the water potential of blood plasma have to be regulated

Answer 9

no net movement of water molecules into the red blood cells and to prevent osmosis, if red blood cell placed in solution with a high water potential then the water molecules will enter the red blood cells then this could burst the red blood cells and cause haemolysis meaning less oxygen will travel around the body to the cells which need to undergo aerobic respiration, if red blood cells are placed in a solution with a lower water potential then the water will move out of the red blood cell then the cell can become crenated

Question 10

what happens to the water potential inside a cell if many ions such as potassium and sodium enter the cell

Answer 10

The water potential decreases

Question 11

What is the consequence of decreasing the water potential within a cell

Answer 11

when the water potential is decreased within a cell, the cell may have a lower water potential than its surroundings this could cause it to enter the cell by osmosis

Question 12

Explain why the onion epidermis cells in distilled water that you observed swell but not burst

Answer 12

onion cells are plant cells therefore they have cell walls these rigid and strong cell walls will prevent the cell from bursting, when the cell has reached its maximum state of swelling the cell wall exerts a pressure preventing any more water from entering

Question 13

explain

• Plasmolysis
• crenation
• haemolysis
• turgid
• flaccid

Answer 13

Plasmolysis - plant cell where the contents has shrunk due to the loss of water by osmosis and the plasma membrane has separated from the cell wall
crenation - a shrivelled animal cell that has lost water by osmosis
haemolysis - lysis of animal cells, in this case it is referring to lysis of red blood cells
turgid - a swollen state of plant cells that have taken in water by osmosis and reached there maximum state of swelling, the cell wall now exerts a pressure which prevents any more water from entering
flaccid - the plant tissue is no longer turgor and the tissue is soft

Question 14

What happens to the water potential inside the cell as water enters the cell by osmosis

Answer 14

The water potential increases

Question 15

In root hair cells nitrate ions are actively transported in from the soil, what is the effect of these nitrate ions on the water potential of the root hair cell and how will it affect osmosis in and out of the cell

Answer 15

• the nitrate ions will reduce the water potential of the root hair cells,
• this would increase osmosis into the cell, this is because the cell would have a lower water potential than the surroundings therefore the water would move down the concentration gradient and across the partially permeable membrane into the cell

Question 16

explain the role of the cytoskeleton in endocytosis and exocytosis

Answer 16

In endocytosis the vesicles are move into the cell using molecular motor proteins along cytoskeleton threads into the cell interior
in exocytosis the vesicles are moved outside the cells by motor proteins moving along cytoskeleton threads to the presynaptic membrane

Question 17

mast cells are present in many tissues and when stimulated by allergens they release chemicals such as histamine from vesicles
A - By what process are these chemicals released
B - does this process use ATP

Answer 17

A - exocytosis
B - yes - ATP is used to fuse the membrane together and to move the vesicles, A molecule of ATP is hydrolysed for every step that a motor protein takes along a cytoskeleton thread

Question 18

A - what can you deduce about how the vacuole of water is emptied by the amobae
B - predict what would happen to the amoebae if the vacuole did not empty at all

Answer 18

A - Removed by exocytosis, the vacuole containing the water is moved to towards the cell surface membrane by motor proteins along a cytoskeleton thread, ATP is used for this, this the cell surface membrane and the membrane of the vesicle are fused together, the fused sites open and release the contents of the secretory vesicle and the water is released
B the cell would burst and by cytolysed as it does not contain a cell wall

Question 19

Compare active transport and facilitated diffusion

Answer 19

Active transport:
- uses energy from ATP from mitochondrial cells 
- against concentration gradient 
- large substances  
facilitated diffusion 
- small polar solutes 
- down concentration gradient 
- go across carrier and channel proteins into the cell