Photosynthesis GEP Science P5

Source: Click on 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: Look at this bird… What is the bird doing?

Source: 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: CO 2 and H 2 O 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: CO 2 + H 2 O C 6 H 12 O 6 + O 2 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 chlorophyll 3.Wash in water. Why must the leaf be boiled in water? To allow I 2 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 I 2 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 CO 2 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 CO 2. 4.Place the other in a bell jar without CO 2 (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 I 2 solution). In which plant will starch be present?

To show that O 2 is given off during photosynthesis 1.Place some water plants eg hydrilla under an inverted filter funnel in a beaker of H 2 O. 2.Dissolve some NaHCO 3 in the H 2 O ( to provide CO 2 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 N 2 to form proteins. 5 Moved to other parts of the plant.

photosynthesis

To test for presence of starch using I 2 solution

To show that CO 2 is needed for photosynthesis

To show that chlorophyll is needed. Use variegated leaf.

To show that O 2 is given off

To show that O 2 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 InputsOutputs 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 Lupus70 beats/min140 beats/min130 beats/min5 min Janus60 beats/min120 beats/min100 beats/min3 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 Lupus70 beats/min140 beats/min130 beats/min5 min Janus60 beats/min120 beats/min100 beats/min3 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 + oxygenwater + 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 airExpired air OxygenAbout 21%About 16.4% Carbon DioxideAbout 0.03%About 4.0% NitrogenAbout 79.0% Water vapourVariable (rarely saturated) saturated TemperatureVariableAbout body temperature Dust particlesUsually presentLittle, 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