Unit 3

Question 1

What is diffusion

Answer 1

. Net movement of particles from a region of higher concentration to region of lower concentration (down a concentration gradient) -> due to their random motion

Question 2

Energy for diffusion

Answer 2

Knietic energy of randome movement of molecules and ions

Question 3

Diffusion in cells

Answer 3

Small molecules can diffuse in and out of cells by diffusion through cell membrane -> allows cells to obtain substances they need (e.g oxygen and nutrients) +get rid of waste products (e.g carbon dioxide)

Question 4

Factors that affect diffusion: Distance

Answer 4

Shorter distance= faster diffusion (e.g cell membrane is very thin)

Question 5

Factors that affect diffusion: concentration gradient

Answer 5

Steep concentration gradient= faster diffusion

Question 6

Factors that affect diffusion: surface area

Answer 6

Larger surface area = faster diffusion

Question 7

Factors that affect diffusion: temperature

Answer 7

Higher temperature= faster diffusion -> more kinetic energy (molecules move faster and collide more often)

Question 8

Water as an important solvent: Transport

Answer 8

. Allows soluble molecules to be carried by blood around body + transports soluble mineral ions from the roots to leaves

Question 9

Water as an important solvent: Digestion

Answer 9

. Digestive enzymes need to be in solution to work properly (water acts as a solvent) + allows products of digestion to dissolve into blood

Question 10

Water as an important solvent: Excretion

Answer 10

Toxins often dissolved in water

Question 11

Osmosis

Answer 11

The net movement of water molecules from an area of high water potential gradient (dilute solution) to an area of lower water porential (concentrated solution) through a partially permeable membrane
. Water diffuses through partially permeable membranes (e.g cell membranes) in both directions by osmosis

Question 12

Osmosis in uptake of water

Answer 12

. Water outside root hair cells usually higher than inside so water diffuses into cells by osmosis

Question 13

Osmosis in loss of water

Answer 13

. Sea water makes water potential in blood much lower than in cells so water leaves cells by osmosis (can shrivel up + die)

Question 14

Investigating osmosis using dyalisis tubing

Answer 14

. Dialysis tubing acts like a partially permeable membrane

Question 15

Investigating osmosis in plant tissues

Answer 15

. If cylinders of potato placed in solution with higher water potential than solution inside potato cells they will draw in water by osmosis + will increase in mass
. If cylinders of potato placed in solution with lower water potential than solution inside potato cells then water will be drawn out by osmosis + will decrease mass

Question 16

Osmosis in plant cells: plant placed in dilute solution

Answer 16

. Inside cell: lower water potential than outside cell -> water diffuses out by osmosis
. As water enters cell starts to swell up -> water pushes against cell wall developing turgor pressure
Turgid cell:
. Gives plants support through turgor pressure on the cell wall
. Cell wall: prevents cell from bursting

Question 17

Osmosis in plant cells: plant placed in concentrated solution

Answer 17

. Inside cell: higher water potential than outside cell -> water diffuses out of cell by osmosis
. As water leavess cell, vacuole starts to shrink -> cells no longer firm and becomes flaccid
. Plasmolysed cell: as more water leaves cell cytoplasm shrinks + cell membrane pulls away from cell wall

Question 18

Osmosis in animals

Answer 18

If animal cell is placed in a solution with high water potential water will move in by osmosis -> if too much water enters there’s nothing stopping the cell from bursting (lack of cell wall)

Question 19

Active transport

Answer 19

Momevent of particles through a cell membrane from a region of lower concentration to higher concentration (against a concentration gradient) using energy release during respiration
. Active transport uses carrier proteins to move particles across the membrane

Question 20

Two substances that are small enough to diffuse through cell membrane

Answer 20

Glucose and amino acids

Question 21

Two substances that are too big to diffuse through cell membrane

Answer 21

Proteins and starch

Question 22

Active transport in plants

Answer 22

Plants need mineral ions for growth
. Higher concentration of mineral ions inside root-hair cells than in soil -> theough active transport high concentration of magnesium ions is mantained in root-hair cell as minerals move against concentration gradients