Movement in and out of cells

Question 1

Why is the cell membrane important?

Answer 1

For ensuring the internal environment of the cell contains the necessary substances at the right concentration for survival

Question 2

What could happen if there was an absence of cell membrane?

Answer 2

The contents of the cell would diffuse out and the substances in the external environment would flow in until the concentrations become equal both intracellularly and extracellularly.

Question 3

Is the cell membrane equally permeable to all substances?

Answer 3

No, as the size and charge of a particle, and whether or not it is lipid-soluble are important factors.

Question 4

What type of molecule passes through the cell membrane easily?

Answer 4

Small uncharged molecules.

Question 5

Explain the input of oxygen for autotrophic and heterotrophic cells:

Answer 5

A: for aerobic respiration when rate of respiration exceeds rate of photosynthesis.
H: for aerobic respiration

Question 6

Explain the input of carbon dioxide for autotrophic and heterotrophic cells:

Answer 6

A: for photosynthesis when the rate of photosynthesis exceeds the rate of respirations
H: not required

Question 7

Explain the output of oxygen for autotrophic and heterotrophic cells:

Answer 7

A: from photosynthesis when rate of photosynthesis exceeds rate of respiration
H: no output

Question 8

Explain the output of carbon dioxide for autotrophic and heterotrophic cells:

Answer 8

A: from respiration and fermentation when rate of photosynthesis exceeds rate of respiration
H: from aerobic respiration

Question 9

Explain the output of lactic acid for autotrophic and heterotrophic cells:

Answer 9

A: not normally produced
H: waste product of fermentation/anaerobic respiration

Question 10

Explain the output of ethanol for autotrophic and heterotrophic cells:

Answer 10

A: a product of fermentation
H: not normally produced

Question 11

Explain the output of ethanol for autotrophic and heterotrophic cells:

Answer 11

A: not normally produced
H: nitrogenous waste product from amino acid breakdown

Question 12

List all the processes for movement into and out of cells.

Answer 12

Diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis.

Question 13

What is diffusion?

Answer 13

The movement of substances from a high concentration to a low concentration until equilibrium occurs. This is a passive process as the particles move with the concentration gradient (no energy is expended).

Question 14

If there is a concentration gradient…

Answer 14

…provided that the cell membrane is permeable to a particular substance, that substance will diffuse across the membrane.

Question 15

How can particles move through the cell membrane if they are unable to move through the phospholipid bilayer?

Answer 15

Channel proteins are able to select and hence move these substances through.

Question 16

How do channel proteins facilitate diffusion?

Answer 16

Channel proteins form open pores in the membrane, allowing small molecules of the appropriate size and charge to pass freely through the phospholipid bilayer.

Question 17

The cell membrane can be described as both…

Answer 17

…semi-permeable and selectively permeable.

Question 18

What is facilitated diffusion?

Answer 18

The use of a channel protein to speed up the diffusion process. These proteins are found in the cell membrane and are able to select molecules, bind with them, and move them through.

Question 19

Is facilitated diffusion passive or active?

Answer 19

Passive since molecules are still moving with the concentration gradient from high to low concentration.

Question 20

What direction is the concentration gradient?

Answer 20

From high to low concentration.

Question 21

What is osmosis?

Answer 21

Refers to the net movement (diffusion) of solvent across a semi-permeable membrane towards a region of higher solute concentration.

Question 22

In osmosis, what is the movement of water dependent on?

Answer 22

The concentration of water molecules and solutes.

Question 23

Is osmosis passive or active?

Answer 23

Passive, as the water molecules move with the concentration gradient through aquaporins (protein channels specific to osmosis).

Question 24

What maintains the shape of an animal cell and provides support in plant cells?

Answer 24

Osmotic pressure, which is defined as the pressure required to stop water from diffusing through a membrane by osmosis.

Question 25

What is tonicity?

Answer 25

It refers to the ability of an extracellular solution to make water move into or out of the cell by osmosis.

Question 26

Define a hypertonic solution.

Answer 26

It has a higher solute concentration; water moves out of the cell.

Question 27

Define a hypotonic solution.

Answer 27

It has a lower solute concentration; water moves into the cell.

Question 28

Define an isotonic solution.

Answer 28

Has the same solute concentration; no net movement of water.

Question 29

What happens o animal cells in a hypotonic solution?

Answer 29

Animal cells will lyse (burst) due to too much water.

Question 30

What is active transport?

Answer 30

The movement of substances against the concentration gradient from a low concentration to a high concentration.

Question 31

What does active transport involve?

Answer 31

A protein carrier and energy (ATP). Transport proteins each have a specific binding site with specific shapes for the substances being transported.

Question 32

What is endocytosis?

Answer 32

The intake of large molecules by enclosing them in a membranous vesicle. During this process, the cell membrane invaginates around the particle, forming a vesicle, which is then taken into the cell.

Question 33

What are the two main types of endocytosis?

Answer 33

Phagocytosis and pinocytosis.

Question 34

What is phagocytosis?

Answer 34

The intake of particles and can be referred to as 'cell eating'. The membrane invaginates in the vicinity of the particle, and encloses it in a vacuole which the breaks away from the cell membrane and enters the cytoplasm. Small mmebrane-bound vesicles containing digestive enzymes then fuse with the 'food vacuole'. These lysosomes the release digestive enzymes that break down the contents of the particle.

Question 35

What is pinocytosis?

Answer 35

'Cell drinking'; involves the intake of liquids or large molecules into tiny vesicles that form at the surface of the cell. It can be non-selective, and involve the intake of extracellular fluid, or it may be selective by involving the intake of large molecules such as fat droplets.

Question 36

What is exocytosis?

Answer 36

The secretion of materials produced y the cell. The substance to be secreted is packaged by the Golgi apparatus into a vesicle, which then moves to the cell membrane with which it fuses, releasing its contents to the outside.

Question 37

What happens to the surface area to volume ratio as a cell increases in size?

Answer 37

It decreases.

Question 38

Why do cells remain small in size?

Answer 38

It ensures a large SA:V and efficiency of nutrient intake and waste removal.

Question 39

What is significant about a higher SA:V?

Answer 39

Higher efficiency for transport of materials across the cell membrane.

Question 40

What happens if the SA:V is too small?

Answer 40

Decreased rate of chemical exchange.

Question 41

Describe the nature of exchange materials.

Answer 41

Small, unchanged particles diffuse easily through the cell membrane, while particles that are too large or charged require assistance from channel proteins, carrier proteins or even whole sections of the membrane.

Question 42

What processes of material exchange are passive and active?

Answer 42

Passive: diffusion, facilitated diffusion and osmosis. Active: active transport, exocytosis and endocytosis.