Life Processes in Plants and Animals

Photosynthesis

Introduction Green plants – have chloroplast containing chlorophyll.

Chlorophyll – enables plant to produce food through photosynthesis.

Some bacteria contains chlorophyll and can photosynthesize

Other bacteria have no chlorophyll, but use energy from chemical processes to make food - chemosynthesis

Producers – organisms able to manufacture their own organic compounds using energy form the sun or chemical reactions

Consumers – organisms who obtain their food by eating other organisms

Decomposers – organisms that cause the decay of dead organisms (Ex: fungi)

Producers can be called autotroph – being able to manufacture their own food

Consumers and decomposers can be called heterotroph- obtain their food from other organisms/sources.

A history of photosynthesis

• Aristotle, who lived more than 2300 years ago, was the first person to suggest that plants get their food from the soil.

• Jan Von Helmont planted a tree, he weighed the tree and the soil before hand.• After a few days he weighed the soil and the tree again, the soil was the same

but the tree was much heavier thus concluding that it was in fact the water in the soil that fed the plant.

• In the 1750’s the people thought that plants only needed water to grow.• In 1771 Joseph Priestly put a sprig of mint in a bell jar for a week, then placed

a burning candle in it. The candle continued to burn, thus plants use carbon dioxide and produce oxygen as the candle needed oxygen to burn.

• In 1773 Jan Ingenhousz showed that plants need light to change the air so that the candle could burn. H also showed that it was green plants who changed the air and that the plants roots also needed air.

• In 1782 Jean Senebier showed that carbon dioxide was used by the plants to “restore” the air.

• In 1804 Nicolas de Saussure showed that plants needed water to make their own food.

• Only in 1950’s did Melvin Calvin discover the biochemical pathway of plants making food.

Process of photosynthesis

Chlorophyll

Light energy from the sun

Water from the soil

Carbon dioxide from the air

Oxygen (waste or by-product)

Organic food for plant (glucose)

1)Requirements for photosynthesis: 2) Products:

Equation of photosynthesis

chlorophyll

6CO2 + 6H2O + light ——————> C6H12O6 + 6O2

enzymes

(catalyst)

chlorophyll

Carbon dioxide + water + light ——————> glucose + oxygen

enzymes

Where does photosynthesis take place? (1) The leaf is the main site for photosynthesis, particularly in the

CHLOROPLASTS (p125)

Chloroplast structure

Where does photosynthesis take place? (2)

Where does photosynthesis take place? (3) The leaf is the main site for photosynthesis

Particularly in the CHLOROPLASTS 2 Phases involved in photosynthesis:

Light reaction/phase Takes place in the grana of chloroplasts

The chlorophyll molecule absorbs light energy

The light energy is used to form the energy-carrier ATP (Adenosine Triphosphate)

The light energy is used to split water molecules to release high energy hydrogen atoms and oxygen.

The hydrogen atoms combine with coenzymes which take them into the dark phase

The oxygen is released into the atmosphere as a by-product (waste)

Dark reaction/phase Take place in the stoma of chloroplasts

Carbon and oxygen from CO2 combines with high-energy hydrogen atoms to form energy-rich carbohydrates (glucose and starch)

The hydrogen and ATP provide the energy for this process

All the reactions of the dark phase is controlled by enzymes

The rate of photosynthesis (1) : Internal factors

Internal factors: The structure of the leaves

Increased rate of photosynthesis in leaves with:

Large and many stomata

Large intercellular spaces (air spaces)

Many mesophyll cells with many chloroplasts

Thin cuticle

Absence/reduced amount of epidermal hairs

Leaves have various adaptations for improved photosynthesis (p131)

The rate of photosynthesis (2): External factors A) Light intensity

Increase in light intensity = increase in photosynthesis

When optimum intensity is reached, rate of photosynthesis levels off because of other factors (not enough water or CO2)

C) Temperature

Optimum temperature = 25˚C in mesophytic plants

As the temperature rises to 25˚C, the rate of photosynthesis increases

Any further increase in temperature (above 25˚C), results in a decrease in photosynthesis because the enzymes become denatured.

B) The carbon dioxide concentration

CO2 concentration in atmosphere – 0.03%

Decrease in CO2 = decrease in photosynthesis

CO2 increase = increase in photosynthesis

High CO2 over long period – decrease in photosynthesis – toxic levels

Water and light may also be limiting factors

A B C

The role of photosynthesis (Importance of photosynthesis)

Most important process on earth. Why?

Primary source of food for all organisms, forms the base of all food chains.

Animals that eat plants are called herbivores.

Provides oxygen for respiration in all living things.

Uses up vast quantities of carbon dioxide produced during respiration, burning of fuels and decomposition

Fossil fuels e.g. coal and oil are derived from plants. Energy stored in these fuels originally trapped from the sun during photosynthesis.

The role of ATP Adenosine Triphosphate (ATP) is a nucleotide that performs

many important roles in the cell: It is the major energy carrier of the cell, providing energy for all

the energy-consuming processes in the cell

It is used in the synthesis of DNA and RNA.

It regulates many biochemical pathways.

It is synthesised in chloroplasts during photosynthesis.

It is also used during the formation of polysaccharides such as starch.

Greenhouses A greenhouse is a special building used for

growing plants in areas (or seasons) where they would not normally grow well.

They have see-through walls and ceilings (polyethylene)

Sunlight passes through the clear walls and ceilings for photosynthesis

It keeps bugs, cold air and birds out.

The plants are watered and fertilised.

A good air flow is also kept flowing (for O2 and CO2).

In commercial greenhouses, trained staff and special equipment monitor and control CO2 levels and humidity.

The role of CO2-enrichment, optimal light and optimal temperature in greenhouse systems

CO2 concentration, light intensity and temperature affect the rate of photosynthesis.

In greenhouses, all these external factors can be increased, decreased or kept constant.

They can use artificial lights or shade cloth to control light intensity.

They can use heaters or fans and shade cloth to control temperature.

They can pump in compressed CO2 to increase the concentration inside the greenhouse.

In this way, special plants can be grown and crop yields can be improved.

Definitions

Photosynthesis

Chlorophyll

Chloroplast

Producer

Autotrophic

Consumer

Heterotrophic

Chemosynthesis

Decomposer

Destarch

Hypothesis

Experiment

Control

Stroma

Lamella

Granum

Light phase

Dark phase

ATP

NADP

Petiole

Stomata

Mesophyll

Palisade mesophyll

Spongy mesophyll

Cuticle

Xylem

Phloem

Greenhouse