Biology paper 2 set 1 SB6?

• plants and algae photosynthesise to make their own food as they are producers and produce their own food.

                                light energy 

carbon dioxide+water -------------> glucose+oxygen

      6CO2         +6H20---------------> C6H12O6+6O2

make sure to remember that when the plants respire they produce carbon dioxide. and they respire all the time. 

• canadian pondweed can be used the measure the effect of light intensity on the rate of photosynthesis.
• the more oxygen there is in the container the faster the rate of photosynthesis 

experiment on next card

• 1.The gas syringe should be empty to start with, sodium hydrocarbonate could be added to the water to make sure that there is enough carbon dioxide in the water.
• 2. A source of white light is placed at a specific distance from the pond weed.
• 3.The pond weed is left to photosynthesise for a certain amount of time, as it photosynthesises the oxygen releaased will be collected in the empty syringe. This allows you to accurately measure the volume of oxygen produced.
• 4. The whole experiment is repeated with the light source at different distances away from the beaker.The rate of oxygen produced at each point was calculated by volume produced by time taken. Variables like temp have to be CONTROLLED

• Light intensity-increases untill its no longer the limiting factor
• Carbon Dioxide Concentration-increases the rate of photosynthesis untill its no longer the limiting factor
• Temperature-increases untill it gets too hot and the enzymes denature, increases the kinetic energy of the molecules and the activity.

light intensity=1/distance(d)squared

Root hair cells 

• Take in minerals and water
• The cells on the surface of plant roots grow into "hairs", each root branch will be covered in millions of these microscopic hairs.
• The millions of hairs give the plant a large surface area for absorbing water and mineral ions in the soil
• The concentration of mineral ions is usually higher in the root hair cells than in the soil around them, so mineral ions and transported by active transport and the water is absorbed by osmosis

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phloem tubes

• transport food
  
• made up of columns of elongated living cells with small pores in the end to allow stuff to flow through
• they transport food substances but they mainly transport sucrose made in the leaves to the rest of the plant for immediate use(e.g in growing regions) or for storage.
• this process is called translocation and it requires energy from respiration.The transport goes in both directions.

xylem tubes

• take water up
• xylem tubes are made up of dead cells joined end to end with no end wall and a hole down the middle.They are strengthened with a material called lignin
  
• they carry water and mineral ions from the roots to the stem and leaves
• the movement of water from the roots, througgh the xylem and out of the leaves is called the transpiration stream.

Transpiration is the loss of water from the plant

• Transpiration is caused by the evapouration and diffusion of water from a plants surface most transpirations happen at the  leaves  
• Because a slight shortage in water has been created due to the loss of water in the leaf more water has to be drawn up from the rest of the plant through the xylem vessels to replace the loss of water
• So therefore this means that more water is drawn up from the roots so there becomes a constant transpiration stream of water through the plant
• The tanspiration stream carries mineral ions that are dissolved in the water along with it.

Stomata which are tiny pores on the surface of a plant are needed for gas exchange

• they are mostly found on the lower surface of leaves
• they allow CO2 and oxygen diffuse in and out of the leaf
• they also allow water vapour to escape during transpiration
• leaves have to have stomata so that gasses can be exchanged easily
• as there is more water inside the plant than in the air outside water escapes from the leaves through the stomata by diffusion.
• stomata are surrounded by guard cells, which change shape to control the size of the pore.TURGID-swollen with water, the stomata are open and when the guardcells are FLACCID-low on water and limp the stomata are closed

Transpiration rate is affected by enviromental factors

• LIGHT INTENSITY-brighter the light faster the transpiration rate as the stomata closes as it gets darker this is becuase photosynthesis cannot happen in the dark so therefore the plant will not need to be letting CO2in to the plant so it can photosynthesise. when the stomata are closed very little water can escape.
• TEMPERATURE-warmer=faster as the particles have more energy to evapourate and diffuse out of the stomata.
• AIR FLOW=the better the air flow around a leaf the greater the transpiration rate as when there poor air flow the water vapour surrounds the leaf and doesn't move away this makes diffusion harder as the concentration gradient is low in comparison when there is a good air flow the water vapour is swept away which maintains a low conc of water on the outside resulting in diffusion happening faster.

Leaves are adapted for photosynthesis and gas exchange by having

• Leaves are broad which means they have a large surface area which is exposed to a lot of light which is needed for the plant to phototsynthesise
• The palisade layer contains a lot of chlorophyll, the palisade layer is located nearer the top of the plant meaning that it can access as much sunlight as possible.
• To help the chlorophyll get as much light as possible the upper epidermis layer is transparent meaning that light can pass through
• The xylem and phloem form a network of vascular bundles this provides the leaf with water which is neded for photosynthesis it also takes away the glucose that is formed from photosythesis. the vascular bundle also helps to support the structure of a leaf.
• The epidermal tissues are covered with a waxy cuticle, the waxy cuticle reduces water loss by evapouration
• The lower epidermis has lots of stomata which lets CO2 diffuse directly into the leaf.
• The spongy mesophyll tissue contains air spaces which increases the rate of diffusion in and out of leaf cells.

cacti tend to have these properties to help them to survive

• small leaves-reduces water loss
• curved leaves-reduces air flow which traps the water vapour
• thick waxy cuticles-reduce the amount of water lost
• a thick stem-storews lots of water
• fewer stomata-to reduce water loss
• stomata suken in pits-makes the stomataa lower than the surface which reduces air flow close to the stomata

Plants produce  chemicals called hormones which regulate growth and development

• Auxins are plant hormones that control thhe growth at shoots and roots.
• they move through the plant in solution
• auxin is produced in the tips and diffuse backwards to stimulate the cell elongation process which occurs in the cells just behind the tips, auxins promtoes growth in the shoot but actually inhibits growth in the root
• auxins are involved in the growth response to light(phototropism) and gravity(gravitropism)

Auxins change the direction of Root and Shoot growth

• Shoots grow towards light so therefore they are positvely phototrophic
• when a shoot tip is exposed to light the side that is in the shade accumulates more auxin.This happens so the cell elongates faster on the shaded side so the shoot bends toward the light.As the plant is getting as much light as it can this means that it can photosynthesise as much as it can and photosynthesis leads to growth of the plant.
• Shoots grow away from gravity so therefore they are negaitvely gravitrophic
• when a shoot is growing sideways gravity produces an unequal distrubution of auxin in the tip with more auxin the the lower side this makes it so the lower side grows faster bending the shoot upwards.

Selective weedkillers

• contain auxins
• weed plants and crop plants compete for water and minerals in the soil
• weeds tend to have broad leaves and broad leaves absorb more of the auxins, auxins stimulate the growth of shoots, too many auxins causes the plant to grow too quickly and die
• as a result of the weeds dying the crop plant gets more water and minerals so grows better

Rooting powder

• Gardeners take cuttings (small pieces) in to new plants.
• They dip the stalk end of the cutting in to rooting powder which contains auxins that cause the stalk to produce roots quickly.
• These cuttings grow in to normal fully developed plants

Gibberellins

• they also stimulate
• stimulate germination of seeds which increases crop yields flower and fruit production which also increasse the yield 
• Gibberellins stimulate stem elongation

Seedless fruit 

• When gibberllins are sprayed on to flowers it can stop seeds beig developed in the fruits 
• They can also make the fruit develop into larger pieces 
• Spraying gibberllins on to fruit can be expensive for the grower