B2.1 Supplying the Cell - Diffusion, Osmosis, Active Transport

Question 1

What is diffusion?

Answer 1

The passive net overall movement of particles from a region of high concentration to a region of low concentration down the concentration gradient.

Question 2

Particles move ……. and …….. by diffusion.

Answer 2

Particles move constantly and randomly by diffusion

Question 3

What key gases do we need to diffuse from our lungs to our blood stream?

Answer 3

Oxygen

Question 4

What key nutrient do we need to diffuse from our blood stream to our muscle cells?

Answer 4

Glucose

Question 5

What factors affect diffusion?

Answer 5

Surface area

Temperature

Concentration gradient

Distance

Question 6

Name key adaptations of the body to facillitate diffusion?

Answer 6

Alveoli

• They are very thin - small distance to diffuse over
• They are covered by a network of fine capillaries - diffuse straight into bloodstream, maintains concentration gradient
• They are moist
• They have a large combined surface area.

Small intestines

• Villi & Microvilli - increases surface area, therefore volume that can be absorbed
• Good blood supply – substances diffuse straight into the bloodstream, maintains concentration gradient

Question 7

What role does diffusion play in nerve impulses?

Answer 7

• Diffusion allows a nerve impulse to travel between two neurones at a synapse
• Neurotransmitter molecules diffuse from vesicles towards the neurotransmitter receptors, moving from an area of high concentration to low concentration.

Question 8

How the is placental organ is adapted to maximise diffusion?

Answer 8

• A large surface area between it and the uterus wall.
• Villi (finger like projections that extend into the uterus wall), which further increase the surface area of the placenta.
• A rich supply of maternal blood vessels.

Question 9

What role does diffusion play in enabling photosynthesis?

Answer 9

• Carbon dioxide diffuses in through the stomata.
• Oxygen and water diffuse out of the stomata
• During photosynthesis, the level of CO₂ is low inside the leaf, creating a big concentration gradient so CO₂ diffuses into the cell

Question 10

Define osmosis.

Answer 10

Osmosis is a special type of diffusion. The diffusion of water molecules across a partially (selectively) permeable membrane from an area of high water potential to an area of lower water potential (down a water potential gradient).

Question 11

What is meant by ‘hypertonic’?

Answer 11

A fluid has a higher osmotic pressure (lower water potential) than a particular fluid, typically a body fluid or intracellular fluid.

Question 12

What is meant by the term ‘hypotonic’?

Answer 12

A fluid has a lower osmotic pressure (higher water potential) than a particular fluid, typically a body fluid or intracellular fluid.

Question 13

Why is osmosis important to plant cells in particular?

Answer 13

The vacuole which helps mantain the cells structure is filled by osmosis.

Question 14

Explain the term ‘turgid’.

Answer 14

When water enters the cell by osmosis and fills the vacuole. This pushes against the cell wall, making the cell turgid.

Question 15

Explain the term ‘flaccid’.

Answer 15

When water moves out of the cell by osmosis, the vacuole shrinks and the cell becomes flaccid

Question 16

This happens if too much water leaves a plant cell, and the cytoplasm moves away from the cell wall.

Answer 16

Plasmolysis

Question 17

What is an isotonic solution?

Answer 17

An isotonic solution is one that has the same osmolarity, or solute concentration, as another solution.

Question 18

What is ‘lysis’?

Answer 18

When an animal cell is placed in a hypotonic solution causing too much water to enter the cell by osmosis and the cell to swell and burst.

Question 19

What is ‘crenation’?

Answer 19

When an animal cell is placed in a hypertonic solution causing too much water to leave the cell by osmosis and the cell to shrink and shrivel.

Question 20

Osmosis takes place over a…

Answer 20

Selectively/semi-permeable membrane

Question 21

Define active transport.

Answer 21

The transport of particles from an area of low concentration to an area of high concentration, against a concentration gradient using ATP (energy).

Question 22

What are carrier proteins?

Answer 22

• Protiens embembedded within the cell surface membrane.
• They bind with useful molecules and then use ATP to rotate or change shape to transport the molecule into the cell.
• Allow the transport of useful molecules against a concentration gratient

Question 23

State an example of active transport in plants.

Answer 23

Root hair cells - Transport of mineral ions from low concentration in the soil to higher concentration in the root hair cell.

Question 24

State two examples of active transport in animals.

Answer 24

1. Nerve cells - active transport used to pump sodium & potassium ions required to create nerve impulses
2. Digestion - active transport used to transport the final products of digestion into the bloodstream through the villi

Question 25

Why do cells that carry out active transport contain a lot of mitochondria?

Answer 25

Mitochondira produce energy and energy is required for active transport to take place.