e) Nutrition

2.17 describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy

Photosynthesis is the process that uses energy (from the sunlight) to create food for itself in the form of glucose. The process occurs inside the chloroplasts of the plant (inside the leaf), which contains a pigment called chlorophyll that absorbs sunlight and uses its energy to convert carbon dioxide and water into glucose. Oxygen is also produced. It is an important process because it converts light energy to chemical energy. which is then released during respiration. 

2.18 write the word equation and the balanced chemical symbol equation for

photosynthesis
                                                           (sunlight)                    

   carbon dioxide      +       water            >             glucose       +    oxygen 

                                                         (chlorophyll) 

         6CO2                 +        6H2O        >           C6H12O6      +    6O2

2.19 understand how varying carbon dioxide concentration, light intensity and

temperature affect the rate of photosynthesis

Carbon dioxide concentration

CO2 is a raw material needed in the process of photosynthesis. If there is too little carbon dioxide present, then the rate of photosynthesis will slow down.  Increasing the concentration of CO2 will also increase the rate of photosynthesis up to a point, until CO2 will no longer be the limiting factor and it will instead be the temperature or the light intensity. 

Light intensity 

Not enough light slows down the rate of photosynthesis. Chlorophyll uses light energy to perform photosynthesis so it can only take place at the rate that light energy is arriving. If the light intensity is increased, the rate of photosynthesis will increase steadily along with it until it reaches a certain point, where the light intensity will no longer make a difference. Instead, it will be either the CO2 level or the temperature which will be the limiting factor (stop photosynthesis from happening any faster.) 

Temperature

The temperature has to be just right in order for the rate of photosynthesis to increase. As the temperature increases, the rate of photosynthesis will also increase but again, only up to a certain point (usually around or above 45 degrees celcius.) This is because the temperature affects the enzymes involved, which are denatured when heated past 45 degrees, making the rate of photosynthesis rapidly decrease. However, it is normally the temperature being too low that is the limiting factor. 

2.20 describe the structure of the leaf and explain how it is adapted for photosynthesis

The structure of leaves is geared towards making photosynthesis as achievable and effective for the plant as possible. 

• Leaves are broad, so there is a large area exposed to the sunlight that the plant needs in order for photosynthesis to occur. 
• Majority of the chloroplasts are found in the palisade mesophyll layer, so they are close to the top of the leaf and therefore receive the most sunlight there. 
• The upper epidermis is transparent, light passes through it to the palisade layer. 
• The network of vascular bundles that leaves have contain xylem and phloem (transport vessels). They deliver water and nutrients to every part of the leaf and take away the glucose the leaf produces during photosynthesis. 
• The waxy cuticle of the leaf helps to reduce its water loss by evaporation (water vital for photosynthesis.) 
• Stomata (little holes in base of leaf) let CO2 diffuse directly into the leaf (CO2, or carbon dioxide, also vital for photosynthesis.) 

2.21 understand that plants require mineral ions for growth and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids. 

Plants need certain mineral ions to grow. They get these elements from the soil, and not enough of that particular element will cause a deficiency in the plant. The two examples you need to know: 

Magnesium ions 

- required for making chlorophyll, therefore needed for photosynthesis. 

- not enough magnesium means plants leaves turn yellow. 

Nitrate ions 

- contain nitrogen, which is used for making amino acids and proteins. 

- therefore needed for cell growth, 

- not enough nitrates/nitrogen means plants will be stunted and their leaves will become yellow. 

2.22 describe experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll 

Pondweed can be used for this experiment, in order to measure the effect of light intensity and levels of CO2 and chlorophyll on the rate of photosynthesis. 

1. Place a source of white light at a specific distance from the pondweed. 
2. Having left the pondweed to photosynthesise for a certain amount of time, you will notice that the released oxygen will collect in the capillary tube. 
3. Draw the gas bubbles in the tube up alongside a ruler to measure the length of the gas bubble. (Proportional to amount of CO2 produced.)
4. Then, repeat the experiment with the light source placed at different distances from the pond weed to see how light intensity affects the rate of photosynthesis. Additionally, you could add baking powder to the water, which will increase the CO2 levels, and test a white leaved plant against a green leaved plant (latter will contain chlorophyll.) Measuring the rate of photosynthesis in each case will tell you how each factor affects it. 

d) Movement of substances into and out of cells

d) Movement of substances into and out of cells

2.12 understand definitions of diffusion, osmosis and active transport

• Diffusion = the net movement of particles from an area of higher concentration to an area of lower concentration.
• Osmosis = the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration. (Water will move from a dilute solution to a concentrated solution.)
• Active transport = the movement of particles against a concentration gradient, from an area of lower concentration to an area of higher concentration, using the energy released during respiration. 

2.13 understand that movement of substances into and out of cells can be by

diffusion, osmosis and active transport

The three processes are the ways in which substances move in and out of cells. 

Diffusion occurs in both liquids and gases (particles in these can move about freely). Particles travel from an area of higher concentration to an area of lower concentration. This can be as simple as different gases diffusing through eachother, or could also be the process of particles passing through a cell membrane from their area of high concentration to an area of low concentration. 

     

• Osmosis

Osmosis is another way through which substances move in and out of cells. The water molecules pass through a partially permeable membrane (one with very small holes in it, including the cell membrane) and will travel from its region of higher concentration to its region of lower concentration. Water molecules move about randomly all the time, so they both in both directions through the membrane however there will be more water molecules on one side than the other, so there will be a steady flow of water into the region with fewer water molecules (particles travel into area of lower concentration.) 

• Active transport 

Active transport is the third way through which substances move in and out of cells. In this process, dissolved molecules move across a cell membrane from an area of lower concentration to an area of higher concentration, therefore against the concentration gradient (normally molecules travel from area of higher concentration to area of lower concentration.) For example, in the digestive system, if there is a low concentration of nutrients in the gut and a higher concentration of nutrients in the blood, then nutrients will go against the concentration gradient and travel from the area of lower concentration (gut) to the area of higher concentration (blood.) Carrier proteins pick up specific materials and take them through the cell membrane to the area of higher concentration, in this case the blood. Because the particles must go against the concentration gradient, they need energy to do this and this energy can be received by living organisms by respiration. 

2.13 understand the factors that affect the rate of movement of substances into and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient. 

There are three main factors that affect the rate of movement of substances into and out of cells. These are: 

1. Surface area to volume ratio

The rate of diffusion, osmosis and active transport is higher in cells that have a larger surface area to volume ratio. For example, if a cell has a surface area of 24cm^2 and a volume of 6cm^3, then its surface area to volume ration will be 24:6 = 4:1. 

So, this cell would have a faster rate of movement of substances than one that had a smaller ratio, such as a surface area of 36cm^2 and a volume of 18cm^3, which would have a ratio of 36:18 = 2:1. 

2. Temperature 

As the particles in a substance are heated and get warmer, they have more energy so move about faster. So, as the temperature increases, so does the rate at which substances move in and out of cells. 

3. Concentration gradient

This only applies to diffusion osmosis, not active transport. The larger the difference in concentration of the inside and the outside of the cell, the faster the substances move in and out of the cell. If there are lots more particles on one side of the cell, then there are more to move across. (This side will have the larger concentration, bigger difference in concentration and therefore will have substances moving in and out of it at a fast rate.)

2.14 understand the importance in plants of turgid cells as a means of
support

When a plant is well watered, all of its cells will draw in water by osmosis and become plump and swollen. They are said to have become turgid when this occurs. The contents of the cell will push against the cell wall - this is referred to as turgor pressure. It is this turgor pressure that occurs in turgid cells that helps to support the plant tissues. 

2.15 understand the factors that affect the rate of movement of substances into
and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient

Surface area to volume ratio

The rate of diffusion, osmosis and active transport is higher in cells with a larger surface area to volume ratio. 

Temperature 

When the particles in a substance are heated (get warmer), they move around at a quicker pace and have more energy. Therefore, as the temperature increases, substances move in and out of the cells at a faster rate. 

Concentration gradient

This only effects the rate of diffusion and osmosis, it does not affect the rate of active transport. The bigger the difference in concentration between the inside and the outside of the cell, the faster substances move in and out of a cell. This is because if there are lots more particles on one side than the other, there are more to move across. 

2.16 describe experiments to investigate diffusion and osmosis using living and
non-living systems.

Investigating diffusion in a non-living system

• Put a few drops of coloured substance (eg. green food colouring) into a jar of water.
• Time how long it takes for the food colouring to diffuse and for all of the water to be the same colour (translucent green if green food colouring is used). Expect this to happen after roughly two minutes of adding the drops. 
•      In another container, again add a few drops of food colouring but this time to water that is a different temperature from the first.
•      Time how long it takes for the food colouring to diffuse in this second container than in the first. If the heat of the water was raised the second time, the colour will have moved through the liquid faster and therefore have diffused at a quicker rate. If you decreased the temperature the second time, the heat will be lower so the particles will have less energy and the colour will move through the liquid at a slower rate, with the diffusion therefore having a slower rate of reaction.

1.        

Investigating Osmosis in Living Systems

•     Cut a potato into two roughly identical cylinders.
•     Measure the length of each cylinder for later comparisons.
•     Place one cylinder into a beaker that has just pure water in, and the other into a beaker that has salt water.
•     After half an hour or so, remove the potato cylinders from their respective beakers and remeasure them.
•     If the cylinder is now a bit longer than it was before being placed into the beaker, then they have drawn water in by osmosis. If the cylinder is now shorter, then water has been drawn out by osmosis. 

Investigating osmosis in non-living organisms

•       Tie a wire around one end of some visking tubing (= a partially permeable membrane) and put a glass tube in the other end, fixing the tube around it with wire.
•       Pour some sugar solution down the glass tube into the visking tube.
•         Then, put the visking tubing in a beaker of pure water and measure where the sugar solution comes up to on the glass tube.
•      Leave the tube overnight, and the next day measure where the  liquid is in the glass tube.
•     Water should have been drawn into the vi=sking tubing by osmosis and this will therefore force the liquid up the glass tube. 

• 
  
•