3. Movement In & Out of Cells

Question 1

Diffusion definition

Answer 1

Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration

Question 2

What do molecules move down during diffusion and why?

Answer 2

Molecules move down a concentration gradient, as a result of their random movement

Question 3

How does a cell membrane affect diffusion?

Answer 3

• can restrict the free movement of the molecules
• The cell membrane is a partially permeable membrane – this means it allows some molecules to cross easily, but others with difficulty or not at all

Question 4

How does the cell membrane filter the molecule? (what is it based on)

Answer 4

The simplest sort of selection is based on the size of the molecules

Question 5

What does diffusion help living organisms do

Answer 5

Diffusion helps living organisms to:

• obtain many of their requirements
• get rid of many of their waste products
• carry out gas exchange for respiration

Question 6

What molecules move through the small intestine?

Answer 6

• digested food products:
• glucose
• amino acids
• fatty acids
• glycerol

Question 7

From where to where do substances in the small intestine move from and to?

Answer 7

FROM lumen of small intestine

TO blood / lymph in villi found covering small intestine walls

Question 8

What molecules move through the leaf?

Answer 8

• oxygen
• carbon dioxide
• water vapour

Question 9

From where to where do substances in the leaf move from and to?

Answer 9

O2
- FROM air spaces between mesophyll cells
- TO mitochondria in all cells
CO2
- FROM air spaces between mesophyll cells
- TO chloroplasts in mesophyll cells
WATER VAPOUR
- FROM stomatal pores
- TO air outside stomata

Question 10

What molecules move through the lungs?

Answer 10

oxygen

carbon dioxide

Question 11

From where to where do substances in the lungs move from and to?

Answer 11

O2
- FROM alveolar air space
- TO blood in capillaries around alveoli
CO2
- FROM blood in capillaries around alveoli
- TO alveolar air space

Question 12

What is the Brownian Motion?

Answer 12

Theory that particles move around randomly

Question 13

Where does the energy for diffusion come from?

Answer 13

The energy for diffusion comes from the kinetic energy of this random movement of molecules and ions

Question 14

What factors influence diffusion?

Answer 14

• distance
• temperature
• concentration gradient

Question 15

How does a cells size affect the surface area to volume ratio? What does this affect?

Answer 15

The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface

Question 16

In what ways are cells adapted for diffusion

Answer 16

Many cells which are adapted for diffusion have increased surface area in some way – eg root hair cells in plants (which absorb water and mineral ions) and cells lining the ileum in animals (which absorb the products of digestion)

Question 17

How does distance affect the rate of diffusion?

Answer 17

The smaller the distance molecules have to travel the faster transport will occur

Question 18

Examples of cells being adapted for diffusion (distance factor)

Answer 18

This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible

Question 19

How does temperature affect the rate of diffusion?

Answer 19

• The higher the temperature, the faster molecules move as they have more energy
• This results in more collisions against the cell membrane and therefore a faster rate of movement across them

Question 20

How does the concentration gradient affect the rate of diffusion?

Answer 20

• The greater the difference in concentration either side of the membrane, the faster movement across it will occur
• This is because on the side with the higher concentration, more random collisions against the membrane will occur

Question 21

Osmosis definition

Answer 21

Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Question 22

What property does a cell membrane have which aids in diffusion? How does it help?

Answer 22

The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)

Question 23

What are plant cells that are full of water called?

Answer 23

Plant cells that are turgid are full of water and contain a high turgor pressure (the pressure of the cytoplasm pushing against the cell wall)

Question 24

Why is turgor pressure useful in plant cells?

Answer 24

• This pressure prevents any more water entering the cell by osmosis, even if it is in a solution that has a higher water potential than inside the cytoplasm of the cells
• This prevents the plant cells from taking in too much water and bursting

Question 25

How can water move into plant cells from soil?

Answer 25

• Plant roots are surrounded by soil water and the cytoplasm of root cells has a lower water potential than the soil water
• This means water will move across the cell membrane of root hair cells into the root by osmosis

Question 26

How is a concentration gradient formed in plants?

Answer 26

The water moves across the root from cell to cell by osmosis until it reaches the xylem
Once they enter the xylem they are transported away from the root by the transpiration stream, helping to maintain a concentration gradient between the root cells and the xylem vessels

Question 27

Why are the results of osmosis more severe in animal cells?

Answer 27

As animal cells do not have a supporting cell wall, the results on the cell are more severe

Question 28

What will happen if an animal cell is placed into a strong sugar solution?

Answer 28

If an animal cell is placed into a strong sugar solution (with a lower water potential than the cell), it will lose water by osmosis and become crenated (shrivelled up)

Question 29

What will happen if an animal cell is placed into distilled water?

Answer 29

If an animal cell is placed into distilled water (with a higher water potential than the cell), it will gain water by osmosis and, as it has no cell wall to create turgor pressure, will continue to do so until the cell membrane is stretched too far and it bursts

Question 30

Active transport definition?

Answer 30

Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Question 31

What is specifically needed for only active transport?

Answer 31

Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion)

Question 32

What are examples of active transport?

Answer 32

• uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron
• uptake of ions from soil water by root hair cells in plants

Question 33

How does active transport work?

Answer 33

Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient:

Question 34

Process in steps for active transport

Answer 34

1. Substance combines with carrier protein molecule in the cell membrane
2. Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane
3. Substance released into cell