Cell biology - Transport in cells

Question 1

what is diffusion

Answer 1

the spreading out of particles from an area of high concentration to an area of low concentration ( through the cell membane )

Question 2

where does diffusion happen

Answer 2

it happens in solutions and gases as the particles in these substances are free to move about randomly

Question 3

things affecting the rate of diffusion

Answer 3

• temperature
• concentration gradient ( difference in concentration)
• surface area - as more particles can pass through at once

Question 4

examples of diffusion

Answer 4

• oxygen moving out of a leaf and carbon dioxide moving in
• carbon dioxide and oxygen moving in the blood to the alveolus in the lungs
• liver cells, urea moving out of the kidneys

Question 5

what kind of molecules can pass through a cell membrane

Answer 5

small molecules like oxygen, not large molecules like starch and proteins

Question 6

what is osmosis

Answer 6

• the movement of water molecules across a PARTIALLY PEMEABLE MEMBRANE from a region of high water concentration to a region of lower water concentration

Question 7

what is a partially permeable membrane

Answer 7

a membrane with very small holes in, only allows small molecules past

Question 8

why do water molecules pass both ways through the membrane during osmosis

Answer 8

because the water molecules move about randomly all the time

Question 9

difference between dilute and concentrated

Answer 9

A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules.

Question 10

what is net flow

Answer 10

overall movement

Question 11

describe what happens during osmosis

Answer 11

• because there are more water molecules on one side of the membrane than the other, there’s a steady net flow of water into the region with fewer water molecules, meaning the solution becomes DILUTE

Question 12

examples of osmosis

Answer 12

• Root hair cells, if the soil is wet or moist, will also take up water by osmosis

-red blood cells could:
lose water and shrink, gain water, swell and burst in a more dilute solution

Question 13

what is active transport

Answer 13

Active transport is the net movement of particles against a concentration gradient from a area of low concetration to a high concentration

Question 14

describe active transport in plants

Answer 14

Active transport allows mineral ions to be absorbed into plant root hairs
from very dilute solutions in the soil. Plants require ions for healthy
growth.

Question 15

describe active transport in humans

Answer 15

Active transport allows sugar molecules, which are needed for cell respiration, to be absorbed from the gut and into the blood from the gut, even when the sugar concentration of the blood is higher.

• allows sugar molecules to be absorbed from lower concentrations
  in the gut into the blood which has a higher sugar concentration. Sugar
  molecules are used for cell respiration.

Question 16

what are exchange surfaces

Answer 16

Exchange surfaces are surfaces that are adapted to maximise the efficiency of gas and solute (a substance dissolved in a liquid) exchange across them

Question 17

how are exchange surfaces adapted

Answer 17

• thin membrane so substances have a short diffusion path
• large surface area so lots of substances can diffuse at once
• efficient blood supply
• ventilation to maintain a high concentration gradient

Question 18

examples of exchange surfaces

Answer 18

small intestine - adapted for exchanging nutrients between digested food in the small intestine and blood

lungs - The lungs are adapted for exchanging carbon dioxide and oxygen between the blood and air.

Gills - The gills are adapted for exchanging oxygen that is dissolved in water, with the carbon dioxide in a fish’s bloodstream.

Roots - Roots are adapted for taking up both water and minerals from the soil around them.

Leaves - Leaves are adapted for exchanging carbon dioxide and oxygen between the leaves and the surrounding air.

Question 19

describe how glucose from the small intestine is moved to a muscle cell

Answer 19

• glucose absorbed by diffusion into the bloodstream
• blood delivers glucose to muscles using capillaries

Question 20

why does a higher temperature increase the rate of diffusion

Answer 20

higher temperature gives particles more energy to move around faster

Question 21

how are single celled organisms adapted for diffusion

Answer 21

A single-celled organism has a relatively large surface area to volume
ratio. This allows sufficient transport of molecules into and out of the cell
to meet the needs of the organism.

Question 22

explain why plants are not able to rely in diffusion to absorb mineral ions from the soil

Answer 22

• the concentration of minerals is higher in the plant than in the soul
• so the minerals will move out of the plant by diffusion

Question 23

how does active transport differ to diffusion

Answer 23

• active transport occurs along a concentration gradient but diffusion occurs down a concentration gradient
• active transport needs energy from respiration but diffusion doesnt