Biology Unit 3

Substances can be exchanges by:

Diffusion - net movement of substance from a high concentration to a low concentration via a partially permeable membrane.

Osmosis - net movement of water from a high concentration to a low concentration via a partially permeable membrane.

Active transport - movement of substance from low concentration to a high concentration using energy.

In plants, carbon dioxide, oxygen and water need to be constantly entering and leaving plants.

• Carbon Dioxide - need for photosynthesis, enters leave though air gaps.
• Oxygen - product of photosynthesis, leaves through air gaps.
• Water Vapour - product of photosynthesis, leaves through air gaps.

The problem is that plants lose water through evaporation, so overall; it loses too much water than it gets. That’s why they have guard cells next to the stomata. When the plant loses lots of water the guard cells close up and do not let any more water vapour through and if there is lots of water, the guard cells open and let more water through. This stops the leaves from wilting (drying up and dying). Also, the guard cells, which are light sensitive, close at night to stop water being lost and no photosynthesis occurring.

The lungs are in the 'Thorax', top part of the body.

The air you breathe in goes from:

• Trachea-->Bronchus(the are two Bronchi)-->Bronchioles-->Alveoli

When you breathe in:

• The diaphram contracts/flattens
• The lungs move up and out
• Air is pulled into the lungs

When you breathe out:

• The diaphram returns to domed shape
• The lungs move in and down
• Air is forced out of the lungs

Rajeev Sharma