Photosynthesis

GEP Science P5

Source: http://www.botany.org/bsa/misc/carn.html

Click on http://www.youtube.com/watch?v=Wdr4aAz7pP8&NR=1 to watch the video.

Look at this special plant…

What do you see in the Venus Fly Trap?

What are the Pandas doing?

Look at the Panda …

Source: Microsoft Clip Art

Source: http://www.birdpark.com.sg/

Look at this bird…

What is the bird doing?

Source: http://commons.wikimedia.org/wiki/File:European_honey_bee_extracts_nectar.jpg

Look at this bee…

What is this bee doing?

Humans

Source: Microsoft Clip Art

What are these people doing?

Why is eating so important?

• Can we survive without eating?

• Food gives energy!

• Energy is required for all life processes.

Question

• So where does all that energy from our food come from?

• Energy cannot be created or destroyed, so it must have been converted from a source…

Look at this plant…

Why photosynthesis?

• Photosynthesis is the process by which plants make food in the presence of sunlight.

• What do the plants need when carrying out photosynthesis?

• Sunlight, water, carbon dioxide… and?

• How do we draw the equation for this?

Photosynthesis Equation

Where does photosynthesis take place?

???

Plant nutrition

Method of nutrition used by plants is: photosynthesis.

1. Raw materials needed:

• CO2 and H2O

2. Conditions present:

• chlorophyll and sunlight~

Leaf Structure

To show presence of stomata

Section of leaf

Structure of Stomata

Stomata: open and close

close

open

Photosynthesis

• Summary equation:

• CO2 + H2O C6H12O6 + O2

Products of photosynthesis:

1 sugar (built up to starch for storage)

2 oxygen.

Light, chlorophyll

How to show that plant is photosynthesising

1. Test for presence of starch .

Photosynthesis is the only way a plant can produce this.

2. How to test for starch?

Use iodine solution.

To test a leaf for starch

1. Boil leaf in water.2. Boil leaf in alcohol to remove chlorophyll3. Wash in water .• Why must the leaf be boiled in water?

To allow I2 solution to penetrate cells.• Why must the leaf be decolorised? To allow blue black colour to show up.• Why must the leaf be washed in water? To soften it.

To show that chlorophyll is needed

1 Destarch a potted plant with variegated

leaf by:

2 placing the plant in the light for 48 hrs.

3 Remove a leaf & test for starch.

4 Only the green parts of the leaf give a

dark blue (blue- black) colour with I2

solution.

To show that light is needed

1. Destarch 2 potted plants.

2. Leave 1 in the dark (experimental).

3. Put one in the light (control).

4. All other conditions must be the same.

5. Leave the 2 plants for 48 hrs.

6. Take a leaf from each plant to test for starch

In which plant will starch be present?

To show that CO2 is needed for photosynthesis

1. Destarch 2 potted plants.2. Place 1 plant in a bell jar with a dish of

soda lime to absorb CO2.

4. Place the other in a bell jar without CO2

(Which plant is the control?)5. All other conditions should be the same for both

plants.6. Leave the plants for 48 hrs, then test the leaf for

starch (with I2 solution). In which plant will starch be present?

To show that O2 is given off during photosynthesis

1. Place some water plants eg hydrilla under an inverted filter funnel in a beaker of H2O.

2. Dissolve some NaHCO3 in the H2O ( to provide CO2 to the plant.

3. Place the apparatus in sunlight for 6 hrs. 4. Set up a control in the same way, but left in the

dark.5. Gas bubbles will only be released from the plant

placed in sunlight.6. This gas rekindles a glowing splint.

What happens to sugar formed in photosynthesis

1 Broken down in respiration.

2 Built up into starch for storage.

3 Turned into fats for storage & other uses.

4 Combined with N2 to form proteins.

5 Moved to other parts of the plant.

photosynthesis

To test for presence of starch using I2

solution

To show that CO2 is needed for photosynthesis

To show that chlorophyll is needed.Use variegated leaf.

To show that O2 is given off

To show that O2 is given off.Glowing splint rekindles.

Where does photosynthesis take place?

• Anywhere that contains chlorophyll / chloroplasts!

• Do chloroplasts have to be green?

Respiration

WHERE DOES CELLULAR RESPIRATION TAKE PLACE?

• Cellular Respiration takes place in the m_____________ of plant and animal cells.

• It is well suited for the process because

WHAT ESSENTIAL HAPPENS IN CELLULAR RESPIRATION?

• Let’s work it out.

• What is needed for respiration?

• We know that the ‘main ingredient’ for this process is _________________.

• For the chemical bonds in the glucose to break, we need to add ____________ to oxidise the glucose.

• What are the outputs of respiration?

• The essential output we need is _______.

• The ‘waste’ products of the process are ___________ and ____________.

Equation for Respiration

• Inputs Outputs

• Oxygen + Glucose Carbon Dioxide + Water

releasing Energy

• Try writing out the chemical equation since you know that glucose is ____________, oxygen is _______ , carbon dioxide is _________ and water is ________.

•PAUSE FOR PAIR WORK

•However, carbon dioxide and water need not be wasted.

e.g. plants, desert animals, snails and corals etc.

TYPES OF RESPIRATION

• Cellular respiration can occur in two ways.

• Aerobic respiration occurs in the presence of oxygen.

• This process releases large amounts of energy.

• Most plants and animals respire aerobically.

• Anaerobic respiration occurs in the absence of oxygen.

• Glucose is broken down without the help of oxygen.

• Happens in simple organisms e.g. yeast (a fungus) and certain bacteria.

• This process does not release as much energy so it is not as efficient as aerobic respiration. However, enough energy is released for the simple organisms.

A BIT MORE ABOUT ANAEROBIC RESPIRATION

• Anaerobic respiration occurs in the absence of oxygen.

• E.g. Yeast breaks down glucose to alcohol and carbon dioxide during anaerobic respiration and energy is given out.

• This is known as alcoholic fermentation. This is how alcohol in wines and beers are produced.

• This process is also required for the making of bread.

• Yeast mixed with a dough mixture anaerobically to produce carbon dioxide which causes the dough to rise.

A BIT MORE ABOUT ANAEROBIC RESPIRATION

• Anaerobic respiration can also happen in animals.

• Anaerobic respiration in muscles produces lactic acid which is toxic and can cause cramp.

• Essentially, this happens when not enough oxygen is delivered to the muscle tissue esp. in vigorous exercise.

• An oxygen debt is built up in the muscles.

• Water and lactic acid is produced.

• Lactic acid will cause fatigue and also energy released in this type of respiration is not enough.

• One will have to stop exercising.

• Oxygen debt is then paid back and the lactic acid is converted back to glucose for use again.

A BIT MORE ABOUT ANAEROBIC RESPIRATION

• Anaerobic respiration can also happen in animals.

• Anaerobic respiration in muscles produces lactic acid which is toxic and can cause cramp.

e.g. Look at the following table.

  Before Exercise

During Exercise

1 min after exercise

Time to return to normal

Lupus 70 beats/min 140 beats/min 130 beats/min 5 min

Janus 60 beats/min 120 beats/min 100 beats/min 3 min

• A pair of identical twins decided to measure their pulse rates before, during and after exercise. Lupus has a sedentary job in an office and enjoys watching TV. Janus has a physically demanding job on a building site and likes to play footbal and tennis. They each did two minutes jogging on the spot.

A BIT MORE ABOUT ANAEROBIC RESPIRATION

  Before Exercise

During Exercise

1 min after exercise

Time to return to normal

Lupus 70 beats/min 140 beats/min 130 beats/min 5 min

Janus 60 beats/min 120 beats/min 100 beats/min 3 min

Think about the following questions.

1. Why does the heart beat faster during exercise?

2. Why does Lupus take a longer time to return to normal?

3. Who would be more likely to feel a cramp? Why?

PAUSE FOR PAIR WORK

• What is the word equation for respiration?• Glucose + oxygen water + carbon dioxide

releasing energy• We know that respiration happens in the mitochondria of the

cells. How does glucose and oxygen reach the cells for respiration to take place?

• PAUSE FOR DISCUSSION

Several systems work together to enable respiration to take place.

Let’s find out which ones they are.

RESPIRATION IN ANIMALS

The path of glucose e.g. potato:

• The potato is taken into the mouth and the _______ help to break it up into smaller pieces while the ________ helps to soften and digest the food slightly.

• The partially digested potato travels down the gullet to the stomach.

• In the stomach, further digestion takes place when the potato is mixed with digestive juices.

• The potato moves to the small intestine where it is fully digested to become glucose.Glucose is absorbed into the bloodstream in the small intestine.

• So, respiration requires the

• DIGESTIVE SYSTEM

RESPIRATION IN ANIMALS

• The path of oxygen :

• We require the process of breathing to take in oxygen. The oxygen is then absorbed into the bloodstream in the lungs.

• So, respiration also requires the

• RESPIRATORY SYSTEM

• So is breathing respiration?

RESPIRATION IN ANIMALS

• Finally for the oxygen to get from the lungs to the cells in all parts of the body and for the glucose to get from the small intestines to the cells in all parts of the body, we need the

• CIRCULATORY SYSTEM

RESPIRATION IN PLANTS

• How does glucose get to all cells in plants?

• How does oxygen get to all cells in plants?

PAUSE FOR DISCUSSION

For glucose,

• It gets transported from the leaves to the rest of the plant through special tubes, phloem.

For oxygen,

• Plants carry out simple diffusion of gases. Leaves of course do so through stomata but for the rest of the plant, it is through diffusion. It happens even in roots.

Gaseous Exchange in Plants

• We seldom find leaves giving off carbon dioxide in bright sunlight. Does that mean plants do not respire in the day?

• During photosynthesis, oxygen is set free. Some of it is retained for tissue respiration.

• But in bright sunlight the rate of photosynthesis is much greater than the rate of respiration, hence more oxygen is set free than the cells can retain for respiration.

• Similarly, since the amount of carbon dioxide produced during tissue respiration is not sufficient for food-making, more carbon dioxide has to diffuse into the leaf from the outside atmosphere.

• Respiration occurs continuously, day and night, in all living cells.

Let’s compare respiration and photosynthesis.

RESPIRATION• Energy is liberated• Oxygen is consumed

and carbon dioxide and water given off

• Breakdown of glucose molecules

• Occurs at all times• Not dependent on

sunlight or chlorophyll

PHOTOSYNTHESIS• Energy is stored in

glucose molecules• Oxygen is given off and

carbon dioxide and water are consumed.

• Build up of glucose molecules

• Occurs only in cells containing chlorophyll and in the presence of sunlight.

Let’s compare respiration and burning (combustion).

RESPIRATION• Controlled process• Energy released mainly

in the form of chemical energy

• Energy released step by step in small quantities

• No sudden rise in temperature

• Need enzymes

BURNING• Uncontrolled process• Energy released entirely

in the form of heat and light

• Sudden release of stored energy

• Sudden rise in temperature

• No need catalyst

In what ways are the two processes similar?

Both release stored energy through oxidation.

However, they can be quite different.

Can you remember the composition of expired and inspired air?

Inspired air Expired air

Oxygen About 21% About 16.4%

Carbon Dioxide About 0.03% About 4.0%

Nitrogen About 79.0% About 79.0%

Water vapour Variable (rarely saturated)

saturated

Temperature Variable About body temperature

Dust particles Usually present Little, if any

Some experiments related to respiration

• To show that air is necessary for respiration

• To show that oxygen is taken in by an animal during respiration

• To show that carbon dioxide is given off during respiration

• To show that energy is released during respiration

• To show anaerobic respiration or alcoholic fermentation