Biology AS AQA Unit 2 Exchange and Transport

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 12:46

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Exchange and Transport
Water moves into the roots by
osmosis.
Water moves into the stem
through a water potential
gradient.

The root cells have a thin cell wall
to give a shorter diffusion
pathway.
Water and nitrates are taken in.
Nitrates are converted into
amino acids which make up
proteins.…

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Symplastic Pathway
Takes place across cytoplasm of cortex cells due to osmosis.
Plasmodesmata are tiny openings in the cell wall in which water passes through.
The plasmodesma is filled with a thin strand of cytoplasm which causes a continuum of cytoplasm in a
column, from the root hair cell to…

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MOVEMENT OF WATER UP STEMS
Main force is transpiration (from evaporation)

Out through stomata:
If the humidity of the external air is lower than the internal air of the stomata, water vapour
molecules will diffuse outwards if the stomata are open. This causes the guard cells to become
flaccid, lose…

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Xylem Tissue
Dead cells joined together to form long empty tubes.
Water moves in via pits.
Lignin is waterproof and strong.
Transports water and mineral salts.
Movement in xylem is due to root pressure or capillaries.
Capillary method is the upward movement of a fluid in a narrow bore tube…

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FACTORS AFFECTING TRANSPIRATION:

Light
Stomata are open in the light and closed in the dark as photosynthesis only occurs in the light (and
requires the rapid diffusion of CO)
When stomata are open, water moves out of the leaf into the atmosphere.
Consequently, an increase in light intensity causes an…

Page 6

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MESOPHYTE ­ Normal conditions.
HALOPHYTE ­ Salt marsh conditions (effect of osmosis)


LIMITING WATER LOSS IN PLANTS
XEROPHYTIC PLANTS
Are plants which are adapted to living in areas where their water losses due to transpiration may
exceed their water uptake.

ADAPTATIONS OF THE PLANT:
A THICK CUTICLE:
The thicker the…

Page 7

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Need to conserve water as it easily evaporates from body surface. Therefore they need
waterproof coverings (rigid exoskeleton covered by a waterproof cuticle) and small SA/V
ratio (minimise area in which water is lost).

Respiratory gases move in and out of tracheal system along a diffusion gradient...
When cells are…

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TRANSPORT SYSTEMS IN MAMMALS
Transport medium to transport dissolved chemicals.
Mass transport system.
Unidirectional flow e.g. valves are then used.
Closed tubular system.
Mechanism for moving transport medium is that we have muscles/heart or physical
processes. E.g. evaporation.
Control of flow of transport medium.

BLOOD VESSELS AND THEIR FUNCTIONS
Arteries:…

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ARTERY STRUCTURE RELATED TO ITS FUNCTION:
Muscle layer is thick compared to veins:
This means smaller arteries can be constricted and dilated in order to control the volume of blood
passing through them.

The elastic layer is relatively thick compared to veins:
It is important that pressure is high to…

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To squeeze the red blood cells against the cells at the side of the capillary.
This reduces distance of diffusion pathway hence speeding up diffusion.

They are numerously and highly branched
Provides a large SA for diffusion which provides a fast rate of exchange (of substances).

Smooth inner surface
To…

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