MOVEMENT OF MOLECULES

Movement of Molecules – Revisit and Test it!

Movement of Molecules – Revisit and Test it!

  • Dissolved substances can move across a semi-permeable membrane by diffusion, active transport or osmosis.
  • Diffusion involves gas or liquid molecules moving across a semi-permeable membrane from an area of high concentration to an area of low concentration across a concentration gradient.
  • Osmosis involves water molecules moving across a semi-permeable membrane from an area of high concentration to an area of low concentration across a concentration gradient.
  • Active transport requires energy and involves particles moving against a concentration gradient from an area of low concentration to an area of high concentration.
  • Sports drinks are designed to replace water and glucose which the body quickly loses during exercise.
  • Alveoli in the lungs are designed for efficient gaseous being thin, moist and having a good blood supply. The lungs contain a large number of alveoli thereby increasing their surface area.
  • The small intestine is efficient at transporting food molecules because it has a thin membrane, a large surface area and a good blood supply.
  • When we inhale the intercostal muscles contract causing the ribcage to expand. The diaphragm contracts, becoming flatter. The chest increases in size which makes the pressure in the thorax decrease and air is pulled into the lungs.
  • When we exhale the intercostal muscles relax and the ribcage drops inwards. The diaphragm relaxes and moves upwards. The chest volume decreases causing the pressure in the thorax to increase and so air is pushed out of the lungs.
  • Roots are efficient for absorbing water because the root hairs increase their surface area and are have very thin membranes.
  • Leaves are efficient for gaseous exchange because they’re thin, have a large surface area, contain air spaces and have a large number of stomata.
  • Water leaves plants through transpiration. The rate of transpiration can be increased by heat, dryness and wind.
  • The amount of water lost is controlled by the stomata. Guard cells control the size of the stomata.

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TEST IT – Molecule Movement!

1. There are two alveoli: one alveolus doesn’t contain much oxygen and is surrounded by oxygen molecules while the other alveolus is filled with oxygen molecules.

a) In which alveoli will the oxygen move faster?

b) How is oxygen taken in by cells in the body?

i. osmosis

ii. diffusion

iii. active transport

a) Which structure is which on the diagram?

i. an alveoli

ii. the diaphragm

iii. the ribcage

b) When you breathe in your diaphragm moves __________________________________ and becomes _____________________________

c) When you breathe out your intercostal muscles_____________________________ making your ribcage _____________________________

2. Many athletes drink sports drinks which are specifically designed to replace certain substances lost by the body during exercise. Complete the table below.

Drink type

Ion concentration

Substance taken up by the body faster

IsotonicHypotonic

3. For an experiment on water loss students used a waterproofing agent.

On leaf 1 they put the waterproofing agent on both surfaces.

On leaf 2 they only put it on the lower side.

On leaf 3 they put it on the upper surface.

Then on leaf 4 they put no agent on at all.

The leaves were then placed in separate beakers and weighed at specific intervals.

a) Which leaf would have lost the most water fastest?

b) Which leaf would have lost the least water?

c) How is water lost by the leaf?

d) Explain how and why the results for leaf 2 and leaf 3 would have been different?

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ANSWERS To Molecule Movement

a) The one that doesn’t contain as much oxygen.

b) ii. Diffusion

a) MARK ON DIAGRAM

b) …downwards…flatter

c) …relax…drops in and down

Drink type

Ion concentration

Substance taken up by the body

IsotonicHypotonic Same concentration as bodyLower concentration than the body GlucoseWater

a) Leaf 4

b) Leaf 1

c) Transpiration

d) Leaf 2 would have lost less water because stomata are mainly found on the underside of the leaf