Transport in cells

Question 1

Diffusion definition

Answer 1

The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient across a partially permeable membrane, until equilibrium is reached.
It is a passive process, meaning it requires no energy.

Question 2

Why do some organisms need specialised exchange surfaces ?

Answer 2

Large multicellular organisms have a small SA : V ratio. This means that they have several layers of cells between the centre and the environment. Therefore, substances will take longer to diffuse, and may be used up by outer layers before they reach inner cells.

Question 3

Factors that aid rate of diffusion

Answer 3

Steep concentration gradient
Large surface area to increase site of exchange
Thin membrane to provide short diffusion path.

Question 4

Osmosis defintion

Answer 4

The movement of water molecules from a dilute region to a concentrated region, down a concentration gradient, across a partially permeable membrane.

Question 5

What is a dilute solution ?

Answer 5

When there is a high water concentration

Question 6

What is a concentrated solution ?

Answer 6

When there is a low water concentration

Question 7

Hypotonic solution

Answer 7

More water outside cell than inside
Water moves into cell via osmosis
Dilute solution

Question 8

Hypertonic solution

Answer 8

More water inside the cell than outside
Water leaves cell via osmosis
Concentrated solution

Question 9

Isotonic solution

Answer 9

Equal amounts of water inside + outside the cell
No net movement

Question 10

What happens when an animal cell is in a hypertonic solution ?

Answer 10

Water leaves the cell via osmosis across a PPM
Cell shrivels
CRENATION

Question 11

What happens when an animal cell is in a hypotonic solution ?

Answer 11

Water enters the cell via osmosis across a PPM
Cell burst as too much water moves in
LYSIS

Question 12

What happens when a plant cell is in a hypertonic solution ?

Answer 12

Water leaves the vacuole via osmosis
Some water is left - leaving the cell with a less rigid shape and smaller vacuole
FLACCID
Cell eventually has no/little water left - very small vacuole, cell membrane and cytoplasm pulls away from cell wall
PLASMOLYSED

Question 13

What happens when a plant cell is in a hypotonic solution ?

Answer 13

Water enters the vacuole via osmosis across a PPM
Cell gains lots of water so swells
Will not burst due to rigid cell wall
TURGID

Question 14

What is active transport ?

Answer 14

The net movement of particles from a region of low concentration to high concentration against the concentration gradient across a partially permeable membrane. Requires energy in the form of ATP, released by respiration in the mitochondria

Question 15

Practical method to investigate the effect of concentrations of sugar solutions on the mass of plant tissue

Answer 15

Set up 6 boiling tubes, each containing the same volume of one of the sucrose solutions.Label the boiling tubes.
Prepare 6 potato cylinders using a borer and cut the cylinders to the same length. Gently dry each potato cylinder using a paper towel to remove excess liquid and record its mass before placing it into one of the boiling tubes.
Leave the potato cylinders in the boiling tubes for 40 minutes.
Remove each potato cylinder from its boiling tube, gently remove excess liquid from the surface of the cylinder with a paper towel and record its mass.
If possible, repeat the experiment to obtain multiple values of mass change for each solution.

Question 16

Properties of the waxy cuticle

Answer 16

Water proof
Stops water evaporating out the leaf

Question 17

Properties of the upper epidermis

Answer 17

Protective barrier against damage and pathogens
Translucent - lets light through to palisade mesophyll

Question 18

Properties of palisade mesophyll layer

Answer 18

Site of photosynthesis
Regular box like structure to maximise photosynthesis
Contains 80% of chloroplasts
Chloroplasts lie at the top of the layer

Question 19

Properties of the spongy mesophyll layer

Answer 19

Less tightly packed
Irregular shaped cells
Contains 20% of chloroplasts
Air spaces for gas exchange

Question 20

Properties of lower epidermis

Answer 20

Protective layer
Contain guard cells - open and close stomata, open to let carbon dioxide in for photosynthesis, close to stop water loss

Question 21

Properties of vascular bundle

Answer 21

Contain xylem - transports water and mineral ions
Contains phloem - transports amino acids and sucrose

Question 22

What are xylem ?

Answer 22

Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels.

Question 23

Properties of xylem vessels

Answer 23

Contain no cytoplasm
Have tough walls containing lignin that builds up in spirals in the cell wall. Lignin makes spirals very strong, to withstand the pressure from water and provide support.
The contents and end walls break down to form a hollow centre, called a lumen.

Question 24

What is a transpiration stream ?

Answer 24

The process that carries water and mineral ions from the roots into the leaves ( one direction ).

Question 25

What happens to guard cells in bright light ?

Answer 25

Potassium ions move into the guard cells via active transport This makes the guard cells more concentrated than the surrounding tissues. Water moves into the guard cells via osmosis across a PPM. Cells swell unevenly because the thicker inner cell wall is less flexible than the thinner outer wall.

Question 26

Potometer required practical to measure rate of photosynthesis

Answer 26

The potometer is filled with water.A shoot is cut from a woody plant. The end of the shoot is cut under water to ensure that the xylem remains water-filled and prevents air locks. The shoot is inserted into the rubber tubing at the end of the potometer. The potometer is raised so that a bubble of air is taken up. The potometer is lowered into the water. The distance travelled by the air bubble is recorded over a period of time.

Question 27

Effects of light intensity on transpiration

Answer 27

Increased light = increased rate of photosynthesis Plant needs more CO2, so stomata opens to let gas in. More stomata open = more water lost by transpiration

Question 28

Effects of temperature on transpiration

Answer 28

Increased temperature = increased kinetic energy of water molecules in leaf Water molecules move more so are more likely to be lost via transpiration

Question 29

Effects of humidity on transpiration

Answer 29

High humidity = closer to equilibrium = lower concentration gradient Slows down rate of transpiration

Question 30

Effects of wind speed on transpiration

Answer 30

Carries away water molecules from the leaf. High conc. gradient as lots of water inside, but not outside, so water leaves by transpiration down a concrete. gradient

Question 31

What are phloem ?

Answer 31

Made up of living cells lined end to end. They contain cytoplasm.

Question 32

What does phloem transport ?

Answer 32

Sucrose + amino acids up and down the plant. This is called translocation. Substances are either immediately used up or stored.

Question 33

Where does translocation occur ?

Answer 33

Between where substances are made ( sources ), and where they are used up ( sinks )

Question 34

Where is sugar in plants made ?

Answer 34

The leaf

Question 35

Where is sugar in plants stored ?

Answer 35

In the roots as starch

Question 36

What are companion cells ?

Answer 36

Found along the outside of the phloem vessel. Contain nuclei and mitochondria to provide energy for translocation.

Question 37

What reduces the resistance of flow in phloem vessels ?

Answer 37

Limited amount of cytoplasm No nucleus or vacuole

Question 38

What allows movement of substances through the phloem vessel ?

Answer 38

Perforated sieve plates

Question 39

What allows substances to be transported all around the plant by translocation ?

Answer 39

A two way flow

Question 40

What is repeatability ?

Answer 40

The measure of the likelihood that, having produced one result from an experiment, you can try the same experiment with the same result. A way for researchers to check their own results are true.

Question 41

What is reproducibility ?

Answer 41

Whether results in a paper can be attained by a different research team, using the same method. Shows that the results attained are not artifacts of the unique set up in one research lab.

Question 42

How is light a limiting factor of photosynthesis ?

Answer 42

Increasing light intensity increases the rate of photosynthesis, so light intensity is the limiting factor. After a certain point, increasing light does not increase rate of photosynthesis, meaning that something else is the limiting factor.

Question 43

How is CO2 a limiting factor of photosynthesis ?

Answer 43

Increasing CO2 concentration increases the rate of photosynthesis, so CO2 concentration is the limiting factor. After a certain point, increasing CO2 does not increase rate of photosynthesis, meaning that something else is the limiting factor.

Question 44

How is temperature a limiting factor of photosynthesis ?

Answer 44

Increasing temperature increases rate of photosynthesis, as enzymes and reactants have more kinetic energy, meaning it is the limiting factor. At the optimum temperature, there is the highest rate of photosynthesis. After the optimum temperature, rate decreases as enzymes denature, as there is too much kinetic energy.

Question 45

How is chlorophyll a limiting factor of photosynthesis ?

Answer 45

The more chlorophyll, the higher the rate of photosynthesis as chlorophyll id needed for reactions. Increased amount of glucose = more protein = increased growth.

Question 46

How to test for starch

Answer 46

Mix food with iodine. If present, turns orange to blue/black

Question 47

How to test for glucose

Answer 47

Mix food with Benedict solution, and heat in a hot water bath for 3 minutes. If present, turns blue to a brick red precipitate.

Question 48

How to test for protein

Answer 48

Mix food with biuret solution and leave for 2 minutes. If present, turns blue to purple

Question 49

How to test for lipids

Answer 49

Mix food with ethanol and add to cold water. If present, turns colourless to milky.

Question 50

Effect of temperature on enzymes

Answer 50

As temp increases, kinetic energy increases, meaning more successful collisions. Optimum temp is body temp. Above this, the shape of the active site is changed as bonds are broken ( denatured ). This means the substrate can no longer fit, so the reaction rate is 0.

Question 51

Effect of enzyme concentration on rate of reaction

Answer 51

Increasing enzyme conc. increases the available active sites, therefore increasing the rate of reaction as more successful frequent collisions can occur. This is true until there are more enzymes than substrates, meaning that the limiting factor is the substrate.

Question 52

Effect of pH on enzymes

Answer 52

Enzymes have an optimum pH. If the pH becomes too acidic or alkaline, the rate of reaction will decrease. The incorrect pH will denature an enzyme.