Biology: Photosynthesis

Stages of photosynthesis: Dark Stage

2) Dark Stage -Can take place in the dark -Uses carbon dioxide -Raw materials provided by products of light stage -Hydrogen released from the water molecules in the light stage combines with CO2 to form carbohydrates -Process called reduction of carbon dioxide

Structure of a Leaf (EXTERNAL)

Blade Margin Veins Stipule

Factors Limiting Photosynthesis

light intensity carbon dioxide concentration temperature

Structure of a Leaf (INTERNAL)

waxy cuticle upper epidermis palisade cell spongy mesophyll airspace lower epidermis stomata guard cells

Adaptions of Leaves for Photosynthesis

Color - color is green due to chlorophyll which traps sunlight and gives the leaf its green color Shape + size - flat, large surface allowing maximum absorption of light Thickness - Thin, allowing easy diffusion of CO2 and oxygen Veins - Help support the thin leaf Carry substances to and from the cells in leaves Pores - located at top and bottom of the leaf allows the process of gaseous exchange

Maximizing Growth

Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.

Economics of greenhouses

However, these extra costs (lighting, heat, CO2) only make sense if there is an increased crop yield and it provides extra income for the farmer. The optimum growing conditions should be ascertained given the extra costs and should not exceed the additional income.

temperature

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesize if it gets too hot.

Conditions Controlled in Greenhouses

In greenhouses, conditions are more easily controlled than in open air outside. These can be controlled through the following techniques: • The use of artificial light allows photosynthesis to continue beyond daylight hours. The use of bright lights also provides a higher-than-normal light intensity. • The use of artificial heating allows photosynthesis to continue at an increased rate (keep temperature at optimum). • The use of additional carbon dioxide released into the atmosphere of the greenhouse also allows photosynthesis to continue at an increased rate.

What is Photosynthesis?

Photosynthesis is the process by which green plants, using energy from sunlight, change inorganic substances (water & carbon dioxide) into food. Simple equation 6Co2 + h20 -> CH2O

How does photosynthesis work?

Plants use sunlight and simple substances to produce sugars and oxygen. Water is taken in through the roots and transported through the plant to the leaves. Plants take in carbon dioxide (CO2) from the air through the stomata, or pores in leaves. Chlorophyll is found in the chloroplasts of cells and absorb the sunlight energy needed to change water and carbon dioxide into glucose. Oxygen is released as a waste product and returned to the air through the stomata in the leaves Chemical Formula: 6CO2 + 6H2O--> C6H12O6 + 6O2

Fate of Glucose

Some is made into amino acids which then go on to make protein Some is made into starch &used as an energy store Some is made into sucrose which is then transported to the rest of the plant Some is converted to lipids & used by the plant in cell membranes Some is made into cellulose for cell walls Some reacts with oxygen & releases energy during respiration for cells to live & grow

carbon dioxide concentration

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesize if there is insufficient carbon dioxide.

Products of Photosynthesis

The main product, glucose, needs to be transported from the leaves to the rest of the plant for its nutrition. This is done through phloem tubes. Glucose can also be converted to starch and stored in starch granules in the plant. Oxygen is released as a by-product into the atmosphere.

How internal structures maximize photosynthesis

Waxy cuticle - waterproof layer; prevents water loss and allows light through for photosynthesis Upper epidermis - transparent layer allowing light to pass through palisade layer/cell -Tightly packed layer on palisades cells, packed with chloroplasts to capture light spongy mesophyll layer - loosely arranged allowing CO2 and oxygen to diffuse vascular bundle - Made from xylem & phloem vessels Xylem transports water & minerals into the leaf Phloem transports food substances from the leaf to other parts of the plant lower epidermis - Protects the leaf and contains stomata Controls water movement into & out of the leaf Where most CO2 and O2 move into & out of the leaf stomata - pores that allow CO2 and O2 to move in and out of the leaf

Light intensity

Without enough light, a plant cannot photosynthesize very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Stages of photosynthesis: Light Stage

1) Light Stage -Sunlight is necessary -Chlorophyll in the leaves convert sunlight into chemical energy -Some light energy used to split water molecules into hydrogen and oxygen. -Process known as evolution of oxygen