Exam Survival Guide IGCSE Biology Study Notes
Topic 3
Plant Nutrition and
Transport
Text Book Chapter 6 (p49-63) and 8 (p100-110)
Quick note on the structure of a typical
plant leaf
In order from the top:
1. Cuticle
Stomata: Surrounded by a pair of guard cells.
o Made of wax
Open (when turgid) and close (when flaccid)
to control transpiration and diffusion of
o Waterproofing the leaf
carbon dioxide and oxygen.
o Secreted by cells of the upper epidermis
2. Upper epidermis
o Transparent
o No chloroplasts
o Protect the inner layers of cells in the leaf / act as a barrier to disease organisms
3. Palisade (mesophyll) layer
o Main region for photosynthesis (contains lots of chloroplasts)
o Columnar and in regular arrangement
4. Spongy (mesophyll) layer
o Another region for photosynthesis (contains some chloroplasts)
o Spherical and loosely packed to have air spaces for gas exchange
5. Lower epidermis
o No chloroplasts, except few present in the guard cells
o Protective layer
o Stomata for gas exchange
The Veins – Xylem Vessels and Phloem
Tubes
 Xylem vessels:





Supply the leaves with water and minerals from the roots
Support the plant (wood is made almost entirely of lignified xylem vessels)
Made up of many hollow dead cells, no cytoplasm or nuclei
Have strong cell walls made of cellulose and lignin
They are long, open tubes with no end walls
 Phloem tubes:




Carry away the sucrose and other organic products of photosynthesis
Have partly broken down end walls, forming sieve plates which have small holes in them
The cells are called sieve tube elements which only contain cytoplasm but no nucleus
Each sieve tube element has a companion cell next to it, the companion cells do have a nucleus,
and also contains many other organelles to supply the sieve tube elements with some of the
requirements
The Veins – Xylem Vessels and Phloem
Tubes
 In leaves:
 In stems:
 In roots
Vascular bundle: a vein in a plant, containing xylem vessels and phloem tubes
Note that xylem vessels always located at the top (in leaves) or centre (in stems and
roots) compare to phloem tubes.
Products of glucose form photosynthesis
1.
Glucose
•
2.
Sucrose
•
•
•
•
3.
For storage in leaves (chloroplasts) and roots
Protein
•
•
•
5.
For growth of shoots
For production of fruits and storage in fruits
For growth of roots
For transport (in phloem tubes)
Starch
•
4.
For respiration
Glucose + nitrate ions or ammonium ions
Deficiency: weak growth, yellow leaves -> die, weak stem
Amino acids are used to make cytoplasm and enzymes
Chlorophyll
•
•
•
•
Glucose + magnesium ions
Deficiency: yellowing between the veins of the leaves
Chlorophyll is needed to trap sunlight for photosynthesis
The deficiency can lead to chlorosis
Reasons why glucose is not suitable for transport and
storage:
 Reactive
 Soluble
 Small molecule
 Affect the concentration gradient when dissolved
in water, could cause wilting
Limiting Factors
• Light intensity  higher the better for but only up to a particular
photosynthesis rate, any higher will not affect the rate
• Carbon dioxide  higher the better for but only up to a particular
photosynthesis rate, any higher will not affect the rate
• Temperature 
• Stomata

High temperature can increase the rate of chemical reactions but
when its too high, the stomata will close to prevent water loss, so
carbon dioxide cannot diffuse into the leaves for photosynthesis
Movement of water
• From the roots: Root hair  Root cortex cells  Xylem  Mesophyll cells
• In the xylem vessels:
1.
2.
The low water potential in the leaves is caused by the loss of water vapour through
the stomata by transpiration. This will create a water potential gradient and pull the
water up.
Water molecules have a strong tendency to stick together called cohesion or capillary
force. When water is pulled up in the long thin xylem vessels, water cohesion keeps
the whole column of water stay together, and causes the water molecules go straight
to the mesophyll layers in the leaves as soon as they enter the xylem vessels.
Factors increase the transpiration rate
1. Increase in temperature  Increase in kinetic energy of water molecules  Water
molecules diffuse out faster, creating low water potential gradient in the leaves
2. Increase in air movement / wind speed  Removes water molecules as soon as they
pass out of the leaf, maintaining a steep concentration gradient (low con. outside) for
diffusion of water vapour
3. Increase in light intensity  Stomata open to allow gas exchange for photosynthesis
 While the stomata open, water vapour can diffuse out of the leaf creating low
water potential gradient
4. Increase in water supply  Provide enough water to continue transpiration [Water
shortage can cause the stomata to close, and therefore the transpiration will stop]
5. Decrease in humidity  Lower water concentration outside the leaves  creating
concentration gradient between inside (higher) and outside (lower) of the leaves 
water moves out, transpiration occurs
Fertilisers
 Replacement of nitrogen ions into the soil:
1. Applying animal manure
2. Crop rotation  growing leguminous plant such as peas, beans and clover every 2
or 3 years; these plants develop root nodules containing nitrogen fixing bacteria
and the roots are ploughed into the soil, boosting nitrate levels
3. Adding artificial fertilisers such as ammonium nitrate
 Dangers of using artificial fertilisers:
1. Wilting and death of the plant  water being drawn out of the plant by osmosis
2. Eutrophication  destruction of life in nearby rivers or lakes  excess growth of
algae  bacteria respire aerobically using dead algae and most of the oxygen in
the river  not much oxygen left in the river, damaging the ecosystem (excess
growth of algae may stop the sunlight getting into the river, use up the oxygen
and nutrients, and the excess wastes may pollute the water and air
Adaptations
 Desert plants
 E.g. cacti and succulents
1. Closing stomata  prevent water loss
2. Waxy cuticle  prevent water loss
3. Hairy leaves  trap moist air (increase “humidity” around the plant), prevent water loss
4. Stomata on underside of the leaves  low temperature, lesser water will evaporate
5. Small surface area  lesser surface for water to evaporate from
6. Deep and spreading roots  for absorption of water
 Water plants
 E.g. water hyacinth
1. Stomata on both sides of the leave  increase photosynthesis rate as more carbon dioxide can
diffuse in (and they do not need to worry about the loss of water)
2. Hollow spaces between stems and leaf stalks  these help the plant gloat on the water where
they can get plenty of light and carbon dioxide for photosynthesis
3. Thin cuticle  they don’t need to worry about the water loss, so they can save the energy and
materials for other uses
Source and Sink
Source  the part of a plant from which sucrose and amino acids are being translocated ; regions of
production or of storage
Sink  the part of the plant to which they are being transloacted ; regions of utilisation in
respiration and growth
Example, a potato plant:
• Summer:
•
•
Source: leaves  photosynthesis  produce glucose
Sink: sucrose and amino acid  translocate to the tubers  stored in the tubers as starch
• Winter:
•
Starch is stored in the tubers during dormant
• Spring:
•
•
Source: tubers  convert starch to sucrose
Sink: sucrose and amino acid  translocate to the new shoots  for growth
Experiments
 For most of the experiments about a plant, you need to destarch it to
ensure that there is no starch stored in the leaves before you do the
experiment. One way is to put the plant under shade to make sure that
it doesn’t produce anymore starch and the starch stored can be used up.
 Testing a leaf for starch: 1, boil the leaf with water or 30s is for breaking
down the cell membranes and cell walls. (so iodine molecules can get
into the cells) 2, Move the leaf into hot ethanol is for removing the
chlorophyll by dissolving it. (so the green pigment won’t affect the
colour change of iodine if starch is present. 3, Put the leaf into a beaker
cool water to soften it before testing it on a white tile with iodine.
Important terms in topic 3
(definitions copy from the text book)
• Photosynthesis: the fundamental process by which plants manufacture carbohydrates from
raw materials using energy from light
• Xylem: long hollow tubes made up of dead, empty cells with lignified walls, which transport
water in plants and help to support them
• Phloem tubes: long tubes made up of living cells with perforated end walls, which transport
sucrose and other substances in plants
• Vascular bundle: a vein in a plant, containing xylem vessels and phloem tubes
• Mesophyll layer: the tissues in the centre of a leaf, where photosynthesis takes place
• Translocation: the movement of sucrose and amino acids in phloem, from regions of
production to regions of storage, or to regions of utilisation in respiration or growth
• Transpiration: evaporation of water at the surface of the mesophyll cells followed by loss of
water vapour from plant leaves (diffusion), through the stomata
• Lignin: a tough, waterproof material that makes up the walls of xylem vessels; wood is mostly
lignin
• Limiting factor: something present in the environment in such short supply that it restricts life
processes
• Systemic pesticides: pesticides that are absorbed into the plant, and translocated in phloem, so
the insects and fungi feeding on the plant can get killed