5.4- Pesticides and Biological Control

understand the reasons for pest control and the advantages and disadvantages of using pesticides and biological control with crop plants

Monoculture: 

• Large fields with the same type of crops
• Susceptible to pests (variety of living things)--> reduces productivity of farming--> loss of food and financial impact on farmer
• Pesticides- Chemical and are designed to kill a pest
• Advantages:
• Chemicals --> Easy to obtain
• Easy to apply
• Very effective
• Disadvantages:
• Very toxic- harmful to humans
• Bio accumulation
• Mutation in the pest leads to resistance
• Pesticides may not work/ may need to be applied in a higher concentration

Biological Control: 

• Cactus flourished in Australia but there were no natural predators of it
• It needed to be removed as it was taking up agricultural land
• Moth (Cactoblastis) was introduced from another country (Alien species)
• Advantages:
• No toxic chemicals involved
• Less impact on humans and wildlife
• Disadvantages:
• Not 100% effective
• Difficult to control
• A danger that an alternative food source might be found for the alien species
• Sometimes difficult to match a predator to the prey

5.3- Fertilisers

understand the use of fertiliser to increase crop yield


Fertilisers:

• Generally take the form of nitrates, phosphates or a combination of both
• These compounds are taken up by the roots 
• Used in the leaf to form proteins (nitrates) and DNA, membrane structure (phosphates)
• Can be divided into two groups:
• Organic
• Produced from animal waste--> Cow faeces
• Goes through decomposition and fermentation
• Forms slurry which gives the plant nitrates and phosphates
• Artificial
• Chemicals which are synthetically produced
• Potassium Nitrate and Ammonium nitrate
• They will go into solution in the soil water
• Releases nitrates 
• Promotes growth in the same way as organic compounds

5.2- Crop yield

understand the effects on crop yield of increased carbon dioxide and increased temperature in glasshouses

Increased concentration of CO2:

• Substrate
• Rate of photosynthesis increases which means that there is a higher yield

Increased temperature:

• Increase in rate of photosynthesis which means that there is a higher yield
• There is an optimum temperature along the graph
• Avoiding frost damage, Constant temperature --> higher yield

Both of the conditions have limits

5.1- Glasshouses

describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops

Glasshouses- Simple house structure, all surfaces are glass which allow light to pass through

1. The initial source of energy is solar radiation
2. Light goes through the glass
3. Light is absorbed by surfaces inside the glasshouse
4. Energy is re-emitted as heat
5. Heat warms the air- raising the temperature
6. Warm air is trapped inside which causes convection currents (warm air rises and moves back down after being cooled at the top of the glasshouse)

Polythene tunnels- Framework with polythene over it, allows light to pass through, cheaper and more adjustable than the glasshouse

Increasing crop yield: 

• High temperatures --> optimum temp. for enzyme reactions (photosynthesis)
• Constant temp. throughout the growing year--> constant production
• Prevention of loss of water vapour --> crops do not dry out
• Avoid frost damage (particularly seedlings)
• Glasshouses are often warmed by burning fossil fuels:
• Increase in carbon dioxide levels inside the glasshouse
• Increased concentration of substrate for photosynthesis
• Production of ethene --> Stimulate fruit ripening

2.89

Understand the sources, roles and effects of the following hormones: ADH, adrenaline, insulin, testosterone, progesterone and oestrogen.


Hormones- Chemicals released by a cell or a gland which sends out messages that affect other parts of the organism. 

• ADH- controls the amount of water in the blood. It is produced in the Pituitary gland. 
• Adrenaline- Increases heart rate and breathing rate during exercise. It is produced in the Adrenal gland.
• Insulin- Decreases the level of glucose in the blood. It is produced in the pancreas. 
• Testosterone- This hormone triggers puberty in boys. It is produced in the testis. 
• Progesterone- Controls the menstrual cycle in females. It is produced in the ovaries.
• Oestrogen- Triggers puberty in girls and stimulates growth of uterus lining. It is also produced in the ovaries. 

2.88

Describe the role of the skin in temperature regulation, with reference to sweating, vasoconstriction and vasodilation

• When the body feels that it is too hot:
• Hairs on skin lie flat (less insulating air trapped)
• Sweating starts
• Blood is diverted close to the surface of the skin (more heat radiation)
• When the body feels that it is too cold:
• Hairs on skin stand up (more insulating air trapped)
• Sweating stops
• Shivering starts, so muscles respire more, producing more heat
• Blood is diverted away from the skin (less heat radiated)
• How is blood diverted?
• Arterioles in the skin can open and close in response to nerve messages
• Vasoconstriction: Arteriole closes
• This happens when the body is cold
• Vasodilation: Arteriole opens
• This happens when the body is hot

2.87

Understand the function of the eye in focusing near and distant objects, and in responding to changes in light intensity

• Eye- Focuses light onto photo receptors
• Photo receptors- the sensory cells of the eyes known as the rods and cones
• When focussing on distant objects:
• The rays of light are almost parallel
• Lens remains flat and focussed on the retina (the inner area of the eye)
• The cilliary body relaxes
• When focussing on near objects:
• The lens has to adjust to the scattered light rays
• The cilliary body contracts which forces the Lens to become rounded
• This allows the image to be focussed on the retina