Chapter Two - Photosynthesis Flashcards
Equation for photosynthesis
6C02 \+ 6H20 | |chorophyll | | light \/ C 6 H 12 0 2
Why are leaves tested for starch?
Leaves convert glucose made during photosynthesis info starch for storage so the test indicates whether photosynthesis has taken place or not.
How is the test for starch made fair? Why is this
First leaves must be destarched by placing the plant in darkness for 48 hours before the plant is exposed to the experimental conditions.
This makes sure any starch detected has been produced during the experiment and was not present before.
Summary of the investigation for photosynthesis
- Boiling the leaf in water
- this stops reactions in the leaf and removes the waxy cuticle - Boiling the leaf in ethanol
- removes chlorophyll to allow iodine colour to be judged more easily - Leaf dipped into hot water
- softens the leaf (as ethanol makes it brittle)
4 iodine added
- a colour change from yellow/brown to blue/black indicates presence of starch, therefore photosynthesis has occurred.
Explain the experiment to show chlorophyll is necessary
Method - use of previously destarched variegated leaves (with white areas that lack chlorophyll) plant left in bright light for two days.
Diagram;
- white edge lacking chlorophyll
- green central area containing chlorophyll
Expected result - White areas should produce negative result (yellow/brown), green areas should produce positive result (blue/black)
Explanation - chlorophyll is needed to absorb light. Areas without it cannot photosynthesis
Explain experiment to show carbon dioxide is necessary
Method - remove carbon dioxide from the air around a previously destarched plant using sodium hydroxide. A second leaf/plant should be set up as a control
Diagram;
- clear plastic bag
- sodium hydroxide solution
- elastic band
Expected result - leaves exposed to air without carbon dioxide should produce negative result
Explanation - c02 is a reactant, if it’s absent the water has nothing to react with so no photosynthesis occurs.
Explain the experiment to show light is necessary
Method - partially covering lead from previously destarched plant with black paper or foil.
Diagram - black paper or foil
Expected result - areas of leaf exposed to light produce positive result (iodine turns blue black). Covered areas produce negative result (iodine remains yellow/brown)
Explanation - light is form of energy required to drive photosynthesis, if light is blocked leaf can’t photosynthesise so no starch is produced.
Explain test for oxygen production during photosynthesis & list the apparatus
A water plant such as Canadian pondweed (elodea) can prove oxygen is made during photosynthesis. It can be show the gas collected is oxygen by using the glowing splint test - oxygen relights a glowing splint.
Apparatus;
- oxygen
- bubbles
- lamp
- water
- water plant
How can elodea be used to investigate the effects of different factors on the rate of photosynthesis
The conditions in which elodea is kept can be altered.
E.g light intensity can be altered by placing the lamp at different distances from the beaker
Label a diagram of a cross section of a leaf from top to bottom
- Cuticle - thin transparent layer, reduces evaporation but allows light through
- Palisade mesophyll - layer rich in palisade cells packed with chloroplasts
- Spongy mesophyll - main gas exchange surfaces, large surface area and moist walls
- Air spaces - for diffusion of gas
- Guard cells - control the opening of the stoma/stomata
- Stoma - can be closed to reduce evaporation of water
Photosynthesis is made more effective by light absorption explain how the leaf is adapted for this.
- leaves are broad and flat to create a large surface area over which light can absorbed
- the palisade mesophyll layer is composed of tall thin cells crammed full of chlorophyll-containing chloroplasts to absorb light energy
- the waxy cuticle is transparent to allow light to enter.
Photosynthesis is made more effective by gas exchange explain how the leaf is adapted for this.
- the spongy mesophyll layer has many intercellular spaces (gaps between cells) to allow gases to move easily from the place where they enter the leaf to the palisade layer.
- the epidermis of the leaf is perforated by many stomata, which are pored through which the carbon dioxide needed for photosynthesis can enter the leaf.
- guard cells surrounding the stoma can change shape in order to control the size of the pore
What difference is there between land and water plants regarding photosynthesis
Most land plants have a higher density of stomata on the underside of the leaf whereas water dwelling plants such as water lilies tend to have more on the upper surface.
Explain the links and differences between photosynthesis and respiration
Link - The products of photosynthesis (glucose and oxygen) can be used for respiration and the carbon dioxide and water released from respiration can be used for photosynthesis
Difference - Light is required for photosynthesis to occur, therefore only occurring during daylight hours whereas respiration takes place at all times in all living organisms.
Colour changes of hydrocarbonate indicator
Turns from red to purple - decreased CO2 so rate of photosynthesis is higher than respiration e.g daylight
Indicator stays red - normal C02, concentration of air (0.04%) e.g dark or dusk
Turns from red to yellow - increased C02 so respiration higher than photosynthesis, no light e.g nighttime
