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Define: photosynthesis

• The process in which green plants make their own food (glucose and starch) using sunlight


Photosynthesis produces glucose for biomass and energy. Oxygen is released as a by product. What is the word and symbol equation for photosynthesis?

Carbon dioxide + water -------> glucose + oxygen
6CO2 + 6H2O ---> C6H12O6 + 6O2


How was the theory of photosynthesis gradually accepted?

• Greeks - plants gained mass by taking in minerals though soil
• Van Helmont - plant growth cannot be solely due to nutrients in soil
• Joseph Priestly - put a plant in a jar if air, and a plant in a jar with a mouse inside. He changed combinations of plants and mouse and concluded that oxygen is produced by plants


Glucose can either be...

• Used straight away to produce energy through respiration
• Converted in substances that the plant needs


What are the properties of glucose?

• Soluble
• Transported around the plant as soluble sugar
• But must be converted into starch, which is insoluble, in order to be stored


Glucose and starch can be converted into:

• Energy (respiration)
• Proteins for growth + repair
• Starch, days or oils that can be stored in seeds
• Cellulose which is needed for plant cell wall


Why is starch such a useful storage molecule?

• Insoluble so it doesn't affect the water concentration inside cells
• It does not move away in solution from storage areas
- If the cells stored soluble glucose, the inside if the cells would become very concentrated and water would constantly move in through osmosis, which would make the cell swell


Photosynthesis can be increased by increasing:

• the temperature - using heaters in a greenhouse
• the light intensity - using lamps in greenhouse
• the carbon dioxide - CO2 concentration is increased by chemicals


Describe the effect of temperature of photosynthesis.

• As temperature rises, so does the rate pd photosynthesis
• This means temperature is the limiting factor in rate of photosynthesis
• As the temperature reaches 45°C, the enzymes controlling photosynthesis start to become denatured
• Once denatured the rate declines to zero


Describe the effect of carbon dioxide concentration on the rate of photosynthesis.

• As the concentration rises, so does the rate of photosynthesis
• Carbon dioxide is limiting the rate of photosynthesis, up until a certain point
• After this point, a rise in carbon dioxide levels makes no difference
• So, carbon dioxide is no longer a limiting factor; light or temperature must be


Describe the effect of flight intensity on the rate of photosynthesis.

• As light intensity rises so does the rate of photosynthesis
• This means light is a limiting factor up to a certain point
• After a certain point, a rise in the light intensity has no effect
• Light intensity is no longer the limiting factor; carbon dioxide or temperature must be


Explain respiration through night and day.

• During the day light is readily available from the sun so plants photosynthesise; taking in carbon dioxide to make glucose and releasing oxygen as a by-product


What is the chlorophyll in a leaf?

• Contains a pigment called chlorophyll (which absorbs light) in millions of chloroplasts
• Plus other pigments to absorb light from different parts of the spectrum


Describe the surface area of a leaf?

• Broad and flat
• Provides huge surface area to absorb sunlight


What do vascular bundles in a leaf do?

• Needed for support and to transport water to the cells
• Removes the products of photosynthesis such as glucose


Why does a leaf have such a thin structure?

• So that gases (carbon dioxide and oxygen) only have a short distance to travel to and from the cells


What does the stomata do?

• Stomata are essentially tiny pores
• On the underside of the leaf to allow the exchange of gases
• They are opened and closed by guard cells


What happens in a plant during photosynthesis?

• Carbon dioxide diffuses in through the stomata (leaf pores)
• Oxygen diffuses out the stomata
• Water is absorbed by the roots


What are the four distinct layers in a leaf?
What are the properties of each layer?

• Upper epidermis - transparent to allow sunlight to the later below
• Palisade layer - where the cells are near to the top of the leaf and are packed with chloroplasts so they can absorb the maximum amount of light
• Spongy mesophyll - contains lots of air spaces connected to the stomata to allow the optimum exchange of gases
• Lower epidermis
* This internal structure provides a high surface area to volume ratio for efficient gas exchange*


What is specialised about the shape of a chloroplast in appellant cell and why aren't they in all plant cells?

• They are long to absorb lots of light
• Not found in all cells
• Such as root cells as they don't receive any light


Define: diffusion

• Substances move in and out of cell membranes by diffusion.
• It's the movement of a substance from a region of high concentration to a region of low concentration


Describe the particle movement in diffusion?

• Particles move about in lots of different directions
• Random movement
• Net (overall) movement of of particles from an area of high concentration to an area of low concentration


What increases the rate of diffusion?

• There's a greater surface area of the cell membrane
• There's a steeper concentration gradient
• The particles have a shorter distance to travel


What do oxygen and carbon dioxide do during the day?

• Carbon dioxide is used up in photosynthesis (The concentration inside the leaves is lower than outside them
• Carbon dioxide diffuses into the plant through the stomata on the underside of the leaf
• Oxygen diffuses from the plant into the atmosphere


What happen to carbon dioxide and oxygen in the night?

• Photosynthesis stops
• Oxygen diffuses into leaf cells
• Carbon dioxide diffuses out of leaf cells
• The stomata on the underside of the leaves are specially adapted to:
- open to help increase the rate of diffusion of carbon dioxide and oxygen
- close to prevent excessive water loss in drought conditions


What are the purposes of the four main mineral essential for healthy plant growth?

• Nitrates - to make amino acids that form proteins
• Potassium - is used to help enzymes in respiration and photosynthesis
• Phosphates - are used to make DNA and cell membranes
• Magnesium - is used to make chlorophyll for photosynthesis


What are the visible results of lack of the four main minerals in plants?

• Lack of nitrates - poor growth, yellow leaves
• Lack of potassium - poor flower + fruit growth, discoloured leaves
• Lack of phosphates - poor root growth, discoloured leaves
• Lack of magnesium - yellow leaves


Define: biological control

• Where a farmer introduces a predator, instead of using pesticide, to reduce the number of pests


Advantages of biological control

• The predator selected only usually attacks the pest (specie specific)
• Once introduced, the predator can have an impact over many years, so repeating treatment isn't required
• The pest can't become resistant to the predator (unlike pesticides)
• No need for chemical pesticides


Disadvantages of biological control

• The pest reduces but isn't completely removed
• The predator may not eat the pest or it may even eat useful species
• The predator may reproduce uncontrollably
• The predator may leave the area


Advantages of hydroponics

• The mineral levels added to the solution can be carefully controlled and adjusted to the type of plant
• The risk if the plants becoming diseased is reduced


Disadvantages of hydroponics

• Plants must be supported as they have no anchorage for their roots
• Expensive fertilisers are needed to supply the plant with minerals


Define: organic farming

• Organic farming methods aims to produce food without the use of chemicals, so minimising the impact on the environment (no pesticides or artificial fertilisers)


List some organic farming methods.

• Using natural fertilisers such as animal manure or compost
• Growing nitrogen-fixing crops such as peas or clover
• Rotating crops to maintain soil fertility
• Avoiding chemical pesticides by weeding
• Varying seed planting times to discourage pests


Advantages of organic farming.

• Food crops and environment aren't damaged by artificial fertilisers and pesticides
• Soil erosion is limited, and fertility is maintained through the use of organic fertilisers
• Biodiversity is promoted because hedgerow and other habitats are conserves
• Livestock have space to roam


Disadvantages of organic farming

• It's less efficient because some crops are lost to pests and diseases
• Organic fertilisers take time to rot and they don't supply a specific balance of materials
• It is expensive
• More space is needed


What are vascular bundles?

• The xylem and phloem form a continuous system of tubes from roots to leaves


What does the xylem do? How are they adapted to do this?

• Transports water and soluble mineral salts from the roots to the leaves (transpiration)
• Xylem vessels are made from dead plant cells. They have a hollow lumen.
• The cellulose cell walls are thickened with a waterproof substances