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PHOTOSYNTHESIS. Plants rule!. Objectives. Define photosynthesis Draw the external & internal structures of a leaf Discuss the factors necessary for photosynthesis. Definitions.
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PHOTOSYNTHESIS Plants rule!
Objectives • Define photosynthesis • Draw the external & internal structures of a leaf • Discuss the factors necessary for photosynthesis
Definitions • AUTOTROPHIC nutrition involves green plants manufacturing organic compounds from simple inorganic substances ( through photosynthesis) • HETEROTROPHIC nutrition involves the feeding of substances made by other organisms.
Autotrophic nutrition • Green plants take in simple substances, which they get from the air and soil. • They use carbon dioxide, water & minerals which are simple inorganic substances. • The plant builds these into more complex materials, such as sugars. • Sugars are organic materials which use sunlight energy.
Photosynthesis sunlight • Carbon + Water Glucose + oxygen dioxide chlorophyll 6CO2 + 6 H2 O C6 H12O6 + 6O2
Chlorophyll • This is the green pigment which makes plants look green. • It is found on the inside of the chloroplasts. • Its role is to absorb the light energy needed for the reaction to take place.
Reactions • Light energy is used to split water molecules into Hydrogen & Oxygen. • O is a waste product given off as a gas. • H is used to join with the components of carbon dioxide to give the organic compound glucose. • Read up on LIGHT & DARK reactions
Glucose • This is the first substance made by plants. • It is a soluble and reactive substance. • Plants convert glucose into starch ( stored form since starch is un-reactive and insoluble) • Glucose molecules join together in chains to form starch molecules. • Starch is not soluble. • However, it is compact ( cannot be broken down easily)
How are the structures in leaf adapted for photosynthesis? • Waxy cuticle • Absence of chloroplast in upper and lower epidermis • Palisade cells packed close together and chloroplast filled vs. spongy mesophyll cells • Spaces between mesophyll cells • Guard cell controlling stoma opening and closing.
How everything get s to chloroplast • CO2 diffuses in through stoma from air. It moves through air spaces in spongy mesophyll to cells and are used by cells during photosynthesis, hence maintaining a diffusion gradient • Water moves by osmosis from soil into plant roots, travels up xylem vessels and moves from cell to cells by osmosis • Light passes across epidermis trapped in chloroplast of palisade cells and chlorophyll uses the energy to split water molecule.
Products of photosynthesis • Glucose is converted to sucrose and transported to other parts of plant where it is converted to carbs, lipids and proteins and used for plant growth • Can be converted to starch and stored in leaf to be used in the night when plant is not photosynthesizing • Converted to starch and stored in storage organs • O2 is waste and some is used fro respiration in leaf while the rest diffuses out
Factors that affect the rate of photosynthesis • Sunlight • Carbon dioxide • Water vapour • Temperature • Stomata functioning • Chlorophyll
Limiting factors • A limiting factor is a component of a reaction that is in ‘shortest supply’ so that is prevents the rate of the reaction from increasing. • LIGHT INTENSITY, CARBON DIOXIDE & TEMPERATURE and WATER AVAILABILITY are all limiting factors. • They limit the rate at which plants can photosynthesize.
LIGHT INTENSITY • Low light intensity lowers the rate of photosynthesis. • As the intensity is increased the rate also increases. • Very high intensity may, in fact, slow down the rate as it bleaches the chlorophyll. • Normal sunlight is quite sufficient for a normal rate of photosynthesis.
Light intensity: • As light intensity increases, the photosynthetic rate increases, until the plant is photosynthesising as fast as it can. (Indicated by a sharp ascent on a line graph) • At this point, if the light becomes brighter, the plant can’t photosynthesise any faster. (Indicated by leveling off on a graph) • Hence during peak sunlight hours (11am – 2pm), photosynthesis will reach at its maximum versus at night when photosynthesis can’t occur.
CARBON DIOXIDE • In the atmosphere, the concentration of carbon dioxide ranges from 0.03 to 0.04 %. • The more carbon dioxide a plant is given, the faster it can photosynthesize up to a point, but then a maximum is reached.
TEMPERATURE • The chemical reactions of photosynthesis will only take place very slowly at low temperatures. • Thus, plants can photosynthesize faster on a warm day than a cold one. • An optimum temperature ranging from 25oC to 35oC is required for a good rate.
WATER Water is an essential factor in photosynthesis. The lack of water not only limits the amount of moisture but also the quantity of carbon dioxide because in response to prevent drying; the leaves close their stomata in order to conserve water being lost as water vapour through them and thereby prevent CO2 from entering.
STOMATA • The carbon dioxide that a plant uses passes into the leaf through the stomata. • If the stomata is closed ( when guard cells are flaccid), then photosynthesis cannot take place. When guard cells are turgid it remains open. • Stomata often closes if the weather is very hot & sunny, this is to prevent too much water being lost ( slows down the reaction) usually when a plant suffers water stress • Stoma also close at night and open in day
Etiolation • If the plant cannot get sunlight it can’t photosynthesise • This doesn’t mean that it cannot continue to grow however • For a short while it uses food that was stored to grow and lengthen in order to reach light.
This gives plant a chance allow leaves to reach sunlight where it can photosynthesize and replace the loss of the stored food. • Growth in the dark causes the cells become thin , elongated and leaves are small and yellow since no chlorophyll is made • If no light is found , it runs out of food reserves and die.
Plant Nutrition • In order for plants to grow and develop they also need inorganic minerals which are usually gained from the soil. • These include nitrogen , phosphorous, potassium, iron, calcium, sulphur and other micronutrients. • These minerals aid in development of different aspects of the plant life and the absence of them can lead to Deficiency diseases developing .
