(U1) Cell Physiology

Question 1

What is simple diffusion? (2)

Answer 1

• The net movement of a substance
• down the concentration gradient

Question 2

What factors affect simple diffusion and how? (5)

Answer 2

• concentration gradient: greater = faster diffusion
• size of molecule: smaller = faster diffusion
• temperature: higher = quicker (more kinetic energy)
• thickness of exchange surface: thinner = faster diffusion
• surface area of membrane: greater SA = faster diffusion

Question 3

What proteins are involved in facilitated diffusion? (2)

Answer 3

• carrier proteins
• channel proteins

Question 4

How do carrier proteins facilitate diffusion? (3)

Answer 4

• take in the polar diffusing molecule
• change shape due to specific receptor sites bonding to the molecule
• release molecules on the other side

Question 5

How do channel proteins facilitate diffusion? (3)

Answer 5

• central pore allows polar molecules to pass through e.g. ions
• some permanently open, others gated
• gated channels open or close to control movement

Question 6

What factor affects the rate of facilitated diffusion that doesn’t affect simple diffusion?

Answer 6

Number of channel or carrier proteins

Question 7

Why does a graph showing increasing concentration and rate of uptake of a membrane for facilitated diffusion level off?

Answer 7

Lack of availability of carrier / channel proteins —> saturated membrane

Question 8

What is active transport? (2)

Answer 8

• net movement of substances against the concentration gradient
• requiring ATP

Question 9

What are the differences between active transport and facilitated diffusion? (2)

Answer 9

• AT: substances moved against concentration gradient, FD opposite
• AT requires ATP, FD does not

Question 10

What does cytosis transport? (2)

Answer 10

• large molecules too big for carrier proteins
• bulk transport of smaller molecules e.g. water

Question 11

What is endocytosis?

Answer 11

Movement of substances into the cell

Question 12

Outline endocytosis (3)

Answer 12

• cell membrane invaginates around substance entering cell
• forming a vesicle which pinches off inside the membrane
• membrane reforms

Question 13

What are the 2 types of endocytosis?

Describe both

Answer 13

• Phagocytosis: transport of solid material into cell e.g. engulfing bacteria by phagocytes
• pinocytosis: transport of fluid into cell

Question 14

What is exocytosis?

Describe it

Answer 14

1. Movement of substances out of the cell
2. • secretory vesicles fuse with cell surface membrane
   • contents of vesicle released outside cell

Question 15

State the equation linking solute potential, water potential and pressure potential

Answer 15

Ψcell = Ψs + Ψp

Water potential of cell = solute potential + pressure potential

Question 16

What is osmosis? (4)

Answer 16

• net movement of water molecules
• through a selectively permeable membrane
• from a solution of less negative water potential / higher water potential
• to a solution of more negative water potential / lower water potential

Question 17

What is the name of channel proteins that allow water through?

Answer 17

Aquaporins

Question 18

What is the difference between hypotonic and hypertonic solutions?

Answer 18

• hypotonic = more water, hypertonic = less water
• hypotonic = lower solute potential, hypertonic = higher solute potential

Question 19

What name is given to 2 solutions of equal concentration / water potential

Answer 19

Isotonic solutions

Question 20

What is water potential? (3)

Answer 20

• tendency to take in water by osmosis
• from pure water
• across a selectively permeable membrane

Question 21

What unit is water potential measured in?

Answer 21

KPa (kilopascals)

Question 22

What the water potential of pure water?

Why?

Answer 22

• 0 kPa
• no water molecules form associations with other molecules

Question 23

What do molecules of water form around solutes?

Answer 23

Hydration shells (largely made up of hydrogen bonds)

Question 24

What is the impact of greater concentration on water potential?

What does this cause?

Answer 24

• More negative water potential
• cell is more likely to take in water by osmosis

Question 25

What is **solute potential**? (**2**)

Answer 25

- potential of a solution to take in water by osmosis - relates to solute concentration

Question 26

What **factor** affects **water potential**, but *doesn’t affect* **solute potential**?

Answer 26

**Space in a cell** which *alters pressure potential* —> turgid cell means lower water potential

Question 27

What is **pressure potential**? (**2**) What **values** can it have?

Answer 27

1. - the *effect of pressure* on the solution - *influences* the **ability** of a **cell to take in water** 2. +ve kPa, but can be 0kPa

Question 28

What **structure** *exerts* **pressure potential** in a *plant cell*?

Answer 28

Cell wall

Question 29

What is **turgor**? (**2**)

Answer 29

- The **force** exerted by the *cell membrane on a cell wall* - by having a **full vacuole**

Question 30

When are **plant cells** described as being **flaccid**? (**2**) On a *large scale* what does this **cause**?

Answer 30

1. - when **cells lack turgor pressure** due to *not having a full vacuole*, - therefore the **cell membrane** *doesn’t press against* the **cell wall** 2. Wilting

Question 31

What is **plasmolysis**? (**3**)

Answer 31

- **vacuole** *loses* water by *osmosis* - *shrinks* the *contents* of the cell - **pulls membrane** *from* the **cell wall**

Question 32

What is **incipient plasmolysis**? (**2**)

Answer 32

- the point at which a **plasmolysed cell membrane** *first makes contact* with the **cell wall** - or the *last time* a **flaccid cell** has its **membrane** *touch* its **cell wall**

Question 33

What is the *effect* of **increasing water potential** *outside a cell* on: - Ψcell - Ψp - Ψs Inside a cell (**2**) ## footnote (*until* **incipient plasmolysis**)

Answer 33

- as cell takes in water, contents become *less concentrated*, **Ψs rises** - **No Ψp** to restrict water uptake as *cell wall isn’t in contact with cell membrane*, therefore **Ψs = Ψcell** (both rise together)

Question 34

What is the *effect* of **increasing water potential** *outside a cell* on: - Ψcell - Ψp - Ψs Inside a cell (**2**) ## footnote (*at* **incipient plasmolysis**)

Answer 34

- **Ψp** becomes **positive** and starts to *hinder water entering the cell* - therefore **Ψcell and Ψs diverge** —> graphs *don’t increase together*

Question 35

What is the *effect* of **increasing water potential** *outside a cell* on: - Ψcell - Ψp - Ψs Inside a cell (**3**) ## footnote (at **full turgor**)

Answer 35

- **max Ψp** between *cell membrane and cell wall* - **Ψcell = 0** —> *no further water can enter* - **Ψs is still negative** as *solutes are still present in the cell*