Section 2 e) Specification

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

Photosynthesis is the process in which plants create glucose and oxygen for respiration from carbon dioxide and water.

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

6 CO2 + 6 H2O --> C6H12O6 + 6 O2
Carbon dioxide + Water --> Glucose + Oxygen

2.19 understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis

Carbon dioxide concentration: Increased CO2 concentration increases rate of photosynthesis as this increases the amount of reactants for this reaction. It will plateau after a while due to limited stomata and chlorophyll.

Light intensity: More intense light increases rate of photosynthesis. Limited by number of chloroplasts.

Temperature: Increases rate of photosynthesis with increased temperature as temp. increases kinetic energy of the particles, leading to more collisions and a faster rate of reaction. The rate of reaction will steadily increase, up until optimum temperature, after which it will drop steeply as it causes enzymes to denature.

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

The leaf is structured in 5 layers:

• Waxy Cuticle: Prevents water loss, protects the plant from damage 
• Upper epidermis: Thin, transparent layer that lets sunlight through to the chloroplasts beneath.
• Palisade mesophyll: Cells are packed full of chloroplasts to absorb as much sunlight as possible. 
• Spongy mesophyll: Contains air spaces that allow gas exchange to occur, maximises surface area for diffusion.
• Lower epidermis: protects the underside of the leaf, has stomata and guard cells that control gas exchange, preventing water loss at night. 

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 require mineral ions for growth, and deficiency can cause a variety of problems:

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

Experiment 1: Oxygen and water plants

1. Choose the variable you wish to change (temp, light intensity, etc.) 
2. Place containers of water and water plants of about the same size in the different conditions. 
3. Count the bubbles that are formed in a certain length of time. 

Experiment 2: Starch and light intensity

1. Put 3 leaves from the same plant of similar sizes in different light conditions: One in a dark room, one in direct sunlight, and one in shaded light. Leave for 48 hours.
2. Test leaves for starch by boiling each in water for 1 minute, then placing in ethanol, then returning it to the water and finally spreading on a petri dish. Add iodine solution to see which leaves test positive for starch 

Experiment 3: Chlorophyll
Test variagated leaves for starch. You can see the green parts test positive for starch while the white parts do not.

Experiment 4: Carbon dioxide
Place a plant in a sealed plastic bag with a container of sodalime (which removes CO2), then test for starch.

Experiment 5: Carbon dioxide
Place water plants in different light levels for 12 hours, with hydrogencarbonate indicator. At the start, indicator should be red, then change to purple for low levels of CO2 (In sunlight) and change to yellow for high levels of CO2 (In darkness)



Humans:
2.23 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre

A human diet must contain a variety of different nutrients in order to be able to carry out necessary functions. The proportions of each group of nutrients is represented by the eatwell plate:

2.24 identify sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fibre as components of the diet

2.25 understand that energy requirements vary with activity levels, age and pregnancy

Generally, the greater a person's mass, the more energy they require. Men are generally larger than women, so they require more energy. Adults require more energy than children because they are much larger. Mid- to late- teens usually require more energy than adults as they are growing, and generally after puberty people will gradually require less and less food as they age. Athletes and people who do more exercise require more energy than people who are less active. Pregnant women require more food, due to growth and increase in mass.

2.26 describe the structures of the human alimentary canal and describe the functions of the mouth, oesophagus, stomach, small intestine, large intestine and pancreas

When food enters the body, it first is mechanically and chemically digested in the mouth. The teeth break up the food to increase its surface area (aiding chemical digestion later on) and to make it easier to swallow, in food bolus. Salivary amylase begins to break down carbohydrates into glucose.
The food is then swallowed, (the epiglottus closes over the trachea to avoid food from falling into the lung) and it travels down the oesophagus through peristalsis: the waves of contraction and relaxation of circular and longitudinal muscles. Peristalsis pushes the bolus of food into the stomach.
The stomach is a large muscular bag that contracts and relaxes to churn the food. The food is held here for 2-4 hours, during this time mixing with gastric juice (a combination of HCl and pepsin, a form of protease), which breaks down protein in the food. The stomach is lined with mucus-producing goblet cells, which helps to prevent the highly acidic HCl from damaging the stomach. Food then passes through into the duodenum.
The duodenum is the first part of the small intestine, it is where digestion is completed. Digestive enzymes (Carbohydrases, proteases and lipases) are secreted in pancreatic juice, from the pancreas. Bile is also released after being made in the liver and stored in the gall bladder. It emulsifies lipids to increase their surface area. The fully digested nutrients are then transported to the ileum.
The ileum is where absorption, or assimilation takes place. The surface of the intestine is folded into tiny villi, which increase the surface area for maximum absorption. It can take place passively, through diffusion, or via active transport. The villi contain capillaries and lacteals (lymph vessels) which absorb digested lipids, amino acids and glucose.
The remaining material is now passed on to the large intestines, the colon. Here, water and mineral ions are reabsorbed. The leftover undigested food, bacteria, etc. (faeces) is stored in the rectum, then egested via the anus.

2.27 understand the processes of ingestion, digestion, absorption, assimilation and egestion

Ingestion: Taking food into the body, eating it.
Digestion: Breaking the food down into nutrients that can be absorbed by the body.
Absorption: Absorbing digested food molecules.
Assimilation: When the absorbed molecules become part of the body, they are used or stored.
Egestion: Discharge of undigested material from the digestive tract.

2.28 explain how and why food is moved through the gut by peristalsis

Peristalsis occurs throughout the entirety of the digestive tract. It works using a series of circular and longitudinal muscles that contract and relax to push the material through.
For example in the oesophagus, when the food enters, the circular muscles contract behind it and the longitudinal muscles relax, pushing the food down. The longitudinal muscles then contract and the circular muscles relax, pushing the bolus further along. This is repeated: the circular muscles contract and the longitudinal muscles relax to move it down, etc. This occurs in waves.

2.29 understand the role of digestive enzymes, to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases

2.30 understand that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids

Bile emulsifies fat, which provides a bigger surface area on which lipase can act. It is an alkali, therefore neutralises acidic stomach acid. Bile is produced in the liver, stored in the gall bladder, and released into the duodenum.

2.31 describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine

Villi are small, hair-like protrusions in the lining of the small intestine. Their shape increases the surface area, helping to absorb nutrients more quickly. Each villus is covered in micro-villi, which further increase the surface area.
The walls of the villi are just one cell thick to decrease the distance and increase the rate of absorption.
Villi each contain a lacteal, a vessel connected to the lymphatic system. This absorbs fatty acids and glycerol, then transports them away from the small intestine.
Each villus contains a network of capillaries connected to blood vessels. Glucose and amino acids are absorbed into the bloodstream through them.

2.32 describe an experiment to investigate the energy content in a food sample.

1. Take a food sample, and light it on fire. Hold beneath a quantity of water with a thermometer in it. 
2. If the sample goes out, quickly relight it. 
3. Note down the temperature rise

Use this equation to calculate the energy content:

energy transferred (J) = mass of water (g) × 4.2 (J/g°C) × temperature increase (°C)