Biology - EDEXCEL IGCSE - Nutrition

Nutrition:

In Plants:

Photosynthesis occurs in plant chloroplasts and is a process where carbon dioxide and water, when there is light, chemically react to form glucose and oxygen. This occurs as light energy is converted to chemical energy, allowing for the reaction to occur.

Testing a leaf for starch:

If there is starch present in the leaf then the plant has been photosynthesising as one of the products of photosynthesis is glucose which is converted to starch for storage.

1.    Boil leaf in water for 2-3 minutes. This is to stop any more reactions such as photosynthesis by denaturing the enzymes. It also opens up all the cell membranes for starch to come out or iodine to go in.

2.    Switch of bunsen burner. Soak leaf in ethanol for 2-3 minutes. The bunsen burner was switched off as ethanol is highly flammable. Ethanol is used to remove chlorophyll, making the leaf milky white and so easier to see what colour the iodine is.

3.    Soak leaf in warm water for 2-3 minutes. This is to soften the lead to allow it to be spread out. It also removes the ethanol.

4.    Spread leaf on a white surface and add 2-3 drops of iodine. It is spread out on the white surface to make the results easier to see. The iodine will turn from red-orange to blue-black if iodine is present.

Release of oxygen in aquatic plants experiment:

1.    Slit the top of the elodea plant used.

2.    Place under funnel in breaker of sodium hydrogen carbonate aqueous solution.

3.    Place measuring cylinder filled with water over funnel after a few minutes and when the elodea plant starts to bubble.

4.    Wait for 1 minute.

5.    Measure how much water has been displaced.

6.    This will give you a result in cm³ / min

7.    You can change factors such as temperature, light intensity, light wavelength and concentration of CO2 to see how this affects the rate of oxygen production.

Factors affecting the rate of photosynthesis:

1.    Temperature - this is related to enzymes. If the temperature is closer to optimum temperature then the rate pf photosynthesis will be higher.

2.    Light intensity - this relates to the light energy that is provided.

3.    Light wavelength - chlorophyll is green so green light will be reflected.

4.    CO2 concentration - this is a requirement for photosynthesis.

5.    Number of chloroplasts - the more chloroplasts available the more light can be absorbed.

Leaf structure and their adaptations:

•    Cuticle - a waxy surface that means water does not congregate on a leaf and therefore means it does not block the light.

•    Upper epidermis - they contain no chloroplasts meaning they are transparent and so allow light to pass through. They are also thin.

•    Palisade cells (mesophyll) - they are long to provide more space for chloroplasts and a large surface area. They are also arranged vertically to stop light refraction away from the chloroplasts.

•    Spongy cells (mesophyll) - they contain air spaces to keep gases and to allow circulation of gases. They also have a circular shape, meaning a large surface area.

•    Xylem, Phloem tubes - there are many of these so that they’re always close to bring water and minerals and to take away sugars.

•    Lower epidermis - contain stomata and guard cells to allow a controlled intake and removal of gases.

A stoma is controlled by 2 guard cells which open and close it. It allows for CO2 to diffuse in and oxygen and water vapour to diffuse out. Stomata is used to get rid of carbon dioxide and oxygen which are created as waste products from metabolism.

When respiration > photosynthesis:

•    CO2 outtake > CO2 intake

•    oxygen intake > oxygen outtake

When photosynthesis > respiration:

•    CO2 intake > CO2 outtake

•    oxygen outtake > oxygen intake

Effects of light intensity of gas exchange:

1.    Wash some pondweed to get rid of small organisms that might respire such as snails.

2.    Place then in 3 test tubes.

3.    Add some equalibrated hydrogen carbonate solution. It was equalibrated to show the surrounding air had normal CO2 concentration.

4.    Place 2 test tube in bright light, 1 in dim and 1 in the dark.

5.    A fourth test tube without the pondweed should be placed in bright light.

6.    After 10 minutes, see what colour the hydrogen carbonate solution is.

Colours of hydrogen carbonate solution:

•    Orange - normal CO2

•    Yellow - Extra CO2

•    Purple - Less CO2

In Humans:

Balanced Diet: eating foods on a regular basis that provide all the right nutrients (carbs, lipids, protein, minerals, vitamins, water and fibre) in the right amount and proportion for the person to remain healthy.

Your diet will change according to your age, whether you’re pregnant, climate and occupation. Your energy requirement will also change according to your activity, age and whether you’re pregnant.

Digestive System:

1.    Mouth - food is ingested, and broken down by the teeth and tongue. Saliva is secreted by the salivary glands which begins the digestion of starch.

2.    Oesophagus - helps food move to the stomach through peristalsis.

3.    Stomach - a muscular bag where food is mixed with hydrochloric acid and pepsin. The acid is used to sterilise the food and create the optimum pH for pepsin to break down protein.

4.    Pancreas - produces pancreatic juices which contains digestive enzymes and hydrogen carbonate which is used to neutralise stomach acids to create the optimum pH for these enzymes to work.

5.    Small Intestine - contains the duodenum where food is mixed with bile and pancreatic juices and the ileum where enzymes complete digestion and digested food is absorbed.

6.    Large Intestine - contains the colon where water and also some vitamins and minerals is absorbed from undigested food. Also contains the rectum which stores undigested faeces.

Nutrient	Where from	Function	Illnesses
Carbohydrates	dessert, table sugar	Needed for respiration to supply energy for cells.	Dental caries such as toothache
Protein	red meats, nuts	Growth, repair and maintenance of cell issue.	Kwashiorkor which causes weakness and tiredness and also a swollen abdomen.
Lipids	butter, eggs	Long term stored energy and insulation.	Coronary heart disease such as angina and heart attacks.
Vitamin A	butter, carrots	Needed for rod and cone cells in the retina.	Nyctalopia - night blindness
Vitamin C	fruit, vegetables (e.g. broccoli)	To make connective tissue that bonds cells together.	Scurvy - bleeding gums
Vitamin D	sunlight, fish liver oil	Needed to take in calcium.	Rickets - deformation of bones
Calcium	dairy, bread	Needed to make teeth and bones.	Rickets - deformation of bones
Iron	eggs, spinach	Helps carry oxygen in haemoglobin.	Anaemia - pale and tired
Fibre	bread, cereal	Allows for the muscles in the gut to have something to push against.	Constipation - infrequent and painful bowel movements
Water	water, fruit	Transports materials and maintains the turgidity of cells.	Dehydration

Bile: produced in the liver, stored in the gall bladder and released into the duodenum. It is used to emulsify/breakdown fats from globules into an emulsion of tiny droplets, giving a larger surface area to volume ratio for lipase to act on. It also neutralises the food.

Peristalsis: a series of muscle contractions that occurs in the gut. When the circular muscle contracts and the longitudinal muscles relaxes the gut narrows. A rhythmic series of narrowing and widening of the gut wall causes the food to be pushed along. Peristalsis needs fibre to work efficiently as this gives the gut something to push against in order to move the food along.

Digestive Enzymes:

Amylase - breaks down starch into maltose. Created in the salivary glands, pancreas and the wall of the gut.

Maltase - breaks down maltose into glucose. Created in the salivary glands, pancreas and the wall of the gut.

Proteases - pepsin and trypsin breaks down proteins into peptides. Peptidases breaks down peptides into amino acids. Both are produced in the stomach wall, pancreas and gut wall.

Lipase - this breaks down lipids into glycerol and fatty acids. Produced in the pancreas.

Feature of the villus	Advantage
Has microvilli	Increases surface area to volume ratio, thereby increasing the rate of diffusion, allowing food to be absorbed quickly.
Circular shape	Again increases surface area to volume ratio.
Steady supply of blood	Maintains a steep concentration gradient.
Epithelium cell only one cell thick	Creates a short diffusion pathway, thereby creating a faster diffusion rate.

Experiment to find energy content of food:

1.    Clamp test tube with 20ml of water and record the temperature.

2.    Set the food alight with a bunsen burner and place the food under the water, relight it if it goes out.

3.    When the food cannot be relit, record the new temperature of the water.

Energy content = (mass of water * temperature change * 4.2) / mass of food

Respiration:

The process of respiration is used to release energy in living organisms. Without respiration energy would not be supplied and therefore many vital functions such as muscle contraction could not occur.

Aerobic respiration - is the respiration which occurs in the presence of oxygen

Anaerobic respiration -  is the respiration which occurs not in the presence of oxygen.