chapter 7 plant nutrition
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Chapter 7 plant nutritionTRANSCRIPT
Chapter 7:Nutrition in Plants
Do Plants Eat?• Like humans, plants need food for energy.
• Where does this food come from?
• It is through the food- making process of Photosynthesis
What is Photosynthesis?
• Photosynthesis is the process in which light energy is absorbed by chlorophyll and converted into chemical energy. The chemical energy is then used to synthesis carbohydrates from carbon dioxide and water. Oxygen is released in the process.
• The raw materials needed: (1) Carbon Dioxide : enters leaves by diffusion, via the stomata
found on the underside of the leaves.(2) Water: enters the plant through the roots and transported to leaves via xylem vessel
Equation of Photosynthesis
Carbon dioxide + Water Glucose + Oxygen + WaterSunlight
Chlorophyll
Light-dependent or light stage
Light-independent or dark stage
light energy chemical energy
H2O12photolysis
of waterO2
6 + 24 H
water oxygen gas hydrogen atoms
CO26 H2O6
watercarbon dioxide
enzyme-controlled reactionsC6H12O6
glucose
+
Overall equation of photosynthesis
CO26 + H2O12
light energy
chlorophyllC6H12O6 + O2
6 H2O6+
Or as a word equation
carbon dioxide + water glucose + oxygen + waterlight energy
chlorophyll
Equations for Photosynthesis
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Where does Photosynthesis take place?
In green leavesIn the mesophyll layers of each leaf
In the cytoplasm of the mesophyll cells
In an organelle called the chloroplast, which contains the green pigment chlorophyll
The Structures involved in Photosynthesis
• CHLOROPHYLL- green pigment that traps solar energy for photosynthesis
• CHLOROPLAST- organelle containing chlorophyll. Chloroplasts are the site of photosynthesis in plants
Internal Structure of the Leaf
(a) Upper Epidermis
(b) Palisade Mesophyll
(c) Spongy Mesophyll
(d) Lower Epidermis
Stoma which is made up of two guard cells
(e)Vascular Bundle
A) Upper epidermis layer – contains no chloroplasts allows sunlight to
pass through easily to the palisade mesophyll layer
– covered with a layer of cuticle reduces evaporation of water
– protects inner layer of cells
B) Palisade mesophyll layer– Main site of photosynthesis contains most number of chloroplasts– Palisade mesophyll cells are long and cylindrical– Cells are packed very closely to one another– During photosynthesis, oxygen will be produced
C) Spongy mesophyll layer– also contains some chloroplasts but main function is not for photosynthesis – main site of gaseous exchange – cells are loosely packed with intercellular air spaces – water will evaporate from surface of spongy mesophyll cells into the air spaces
water vapour in the air spaces will move out of the stomata into surrounding air by diffusion
Gaseous Exchange of water
Diagram showing movement of water out of the leaf
TRANSPIRATION the process where water vapour move out of stomata of leaves
Diagram showing movement of carbon dioxide
Gaseous exchange of Carbon dioxide
During photosynthesis, carbon dioxide from surrounding air will enter the stomata by diffusion into the intercellular air spaces it will then enter the spongy mesophyll cells
Gaseous exchange of Oxygen
Diagram showing movement of oxygen
The opposite happens for oxygen during photosynthesis from spongy mesophyll cells out of the stomata into the surrounding air
D) Lower epidermis layer – same as the upper epidermis EXCEPT that it also contains stomata (small pores) – stomata are always surrounded by two cells called the guard cells – guard cells contain chloroplasts for photosynthesis to occur– guard cells control the stomata, which in turn controls the amount of gases entering and leaving the leaf
(E) Vascular BundleMade up of the:
1) Xylem vessels (always on the top)Function: transport water from the roots to the
palisade mesophyll cells for photosynthesis to take place
- water in the palisade mesophyll cells will ALSO move to the spongy mesophyll cells to escape into the surrounding air
2) Phloem ( always on the bottom) Function: transports food made during photosynthesis
from the palisade mesophyll cells to other parts of the plant
(E) Vascular Bundle
Structure of a Dicotyledonous Leaf
The leaf lamina is very thin. It is made up of only a few layers of cells
Palisade mesophyllCells densely packed together like a ‘fence’ to maximise exposure to sunlight passing through epidermis. Cells contain highest concentration of chloroplasts; main site of photosynthesis
Upper epidermisA single layer of cells which are transparent to allow sunlight to penetrate to mesophyll. No stoma present, minimising water loss
Spongy mesophyllCells more loosely packed, air spaces present to allow penetration of air from stomata to upper layer for gaseous exchange
Lower epidermis‘Pores’ for gaseous exchange present. The pores are called stomata, the opening of each stoma controlled by a pair of guard cellsNo layer of cuticle
The leaf is modified for its main function, which is photosynthesis
Structure of a Dicotyledonous Leaf
Lower epidermis‘Pores’ for gaseous exchange present. The pores are called stomata, the opening of each stoma controlled by a pair of guard cellsNo layer of cuticle
One stoma
Guard cells
Air movement
Surface view
The lower epidermis- Stomata for Gaseous Exchange
What Happens to the Manufactured ‘Food’?
Glucose produced by photosynthesis in leaf is converted to sugars (mainly sucrose) and translocated to different parts of the plant
To growing regions to be used as energy for growth
To storage organ (fruit)to be stored mainly as sugars
To storage organ (tubers in roots)To be stored mainly as starch
Transport in the phloem occurs in both directions up and down the plant (bidirectional movement)
If the plant requires more energy than can be produced, food stores are mobilised, converted back to sugars, and transported to wherever it is needed
The movement of sugars and amino acids via the phloem is called translocation
Glucose
In photosynthesis, carbon dioxide and water form
Used immediately by plant cells• for cellular respiration• to form cellulose cell walls.
1 Converted into sucrose or into starch in leaves• Excess glucose is converted into sucrose and transported to storage organs as starch or in other forms. • In daylight, excess glucose is converted into starch for temporary storage in the leaf. It may be converted into glucose at night or into sucrose and transported away for storage.
2
Used to form amino acids and proteins• Glucose reacts with nitrates to form amino acids in the leaf. • The amino acids are combined to form proteins, which make up new protoplasm in the leaf.• Excess amino acids are transported away for synthesis of new protoplasm or for storage as proteins.
3
Used to form fats• for storage• used in cellular respiration• for synthesis of new protoplasm
4
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Fates of Glucose Formed During Photosynthesis
Factors limiting Photosynthesis• Carbon dioxide concentration
– Carbon dioxide is one of the raw materials needed for photosynthesis. Therefore if there is absence or lack of carbon dioxide, a plant will not be able to photosynthesize. The normal atmospheric concentration is 0.03%.
• Light intensity– Without enough light a plant cannot photosynthesize very fast,
even if there is abundance of water and carbon dioxide. Increasing the light intensity will increase the rate of photosynthesis.
• Temperature – The reactions in photosynthesis are enzyme-dependent. At too
high a temperature they are denatured; at too low a temperature the reactions progress very slowly.
Graphs showing the effect of these three factors on the rate of photosynthesis
Importance of photosynthesis
1) Photosynthesis makes chemical energy available to animals
- Light energy is converted into chemical energy and stored in food.- Carbohydrates produced during photosynthesis is a source of food for all living
organisms
2) Photosynthesis removes carbon dioxide and provides oxygen
- Oxygen is produced for respiration and removes carbon dioxide from the air. - Acts as a purification process.
Light-dependent stage
• light energy chemical energy
• water hydrogen and oxygen
chlorophyllLight-independent stage
• carbon dioxide glucosechemical energy
water
occurs in two stages
light energy
PhotosynthesisFactors affecting photosynthesis• carbon dioxide• sunlight• temperature• water• chlorophyll
Importance of photosynthesis• provides food for animals• stores energy from the sun as chemical energy• maintains the balance oxygen and carbon dioxide in the atmosphere
Fates of glucose
Broken down to release energy for vital activities
Used in synthesis of cell wall
Converted into amino acids and proteins
Converted into fats
Excess stored temporarily as starch in leaves
Glucose
produces
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