Transport across cell membranes : osmosis and active transport

What is osmosis

How does water move? (water potential)

water moves by osmosis from a less negative water potential to a more negative water potential.

What does hypertonic, hypotonic, isotonic mean?

Hypotonic- lower water potential to a cell

Hypertonic- Higher water potential to a cell

Isotonic- Same water poential

What happens if the surrounding solution in an ANIMAL cell is HYPERTONIC

The cell swells and burst as water enters it by osmosis (LYSIS)

What happens if the surrounding solution in a PLANT cell is HYPERTONIC

It becomes turgid because no more water can enter due to the pressure of the cell surface membrane pushing against the cell wall.

What happens if the surrounding solution in an ANIMAL cell is ISOTONIC?

It stays the same

What happens if the surrounding solution in a PLANT cell is ISOTONIC>

Stays the same

What happens if the surrounding solution in a PLANT cell is HYPOTONIC?

The cell becomes plasmolysed which is when the protoplast (nucleus and vacuole) shrink from the cell wall

What happens when the surrounding solution in an ANIMAL cell is HYPOTONIC

The cell shrinks and crenates.(formation of uneven corners)

What does active transport mean?

The movement of molecules or ions from a region of low concentration to high concentration against the concentration gradient.

What does active transport require?

ATP and carrier proteins

What is the main difference between facilitated diffusion and active transport?

1. it requires ATP from respiration in photosynthesis

2. its against the concentration gradient]

3. Its selective and specific

describe how active transport work?

1. A molecule or ion binds to a receptor site on a carrier protein

2. on the other side of the carrier protein, ATP binds to the carrier protein

3. ATP is then hydrolysed into ADP+ pi this catalysed by ATP hydrolase. This causes the protein to change shape and the other side opens and the originally open side closes.

4. The molecule or ion is released onto the other side of the membrane

5. The phosphate ion (pi) is released from the protein meaning the protein retains its original shape

6. The phosphate ion and ADP are recombined during respiration or photsynthesis to from ADP

Why do we need co transport for the absorption of glucose?

The facilitated diffusion will result in equilibrium so not all glucose will be absorbed by facilitated diffusion so co transport is needed.

Where does co transport take place?

In the ileum (final part of the small intestine) where concentration of glucose is too low for it to diffuse into the blood.

How are cell adapted for rapids transports across the membranes?

Large SA

Thin membrane= Short diffusion path

Large number of carrier and channel proteins to increase the rate of facilitated diffusion and active transport