Section 2 e) Summary

Flowering Plants
Plants don't need to eat, they get all of their nutrients by absorbing mineral ions from the soil, and carrying out photosynthesis.
Photosynthesis is the process by which plants generate glucose (which is stored as starch) using sunlight:

Carbon dioxide + Water -(sunlight)-> Glucose + Oxygen
6CO2 + 6H2O -(light energy)-> C6H12O6 + 6O2

They are able to do this because their cells contain organelles called chloroplasts, which contain a green pigment known as chlorophyll. Chlorophyll is the chemical that carries out photosynthesis.

Factors affecting photosynthesis:

• Temperature: As temp. increases, the particles move faster and the rate of photosynthesis is increased, but after reaching optimum temperature for the enzymes they begin to denature at any higher temp. and the rate of photosynthesis drops steeply.
• Light intensity: More intense light means more photosynthesis, but only up until a certain point as the number of chloroplasts is limited.
• Carbon dioxide concentration: Higher concentrations of CO2 mean more photosynthesis, but only up until a certain point as the number of chloroplasts is limited.
• Chlorophyll: Variagated leaves will photosynthesize less than single coloured leaves, lighter coloured leaves will photosynthesize less than darker ones due to the number of chloroplasts available to carry out photosynthesis

The diagram below shows the structure of a leaf

 Each layer has a different function:
The waxy cuticle protects the cell from damage, and prevents water loss.
The upper epidermis is thin and clear, and provides a layer of protection.
The palisade mesophyll is made up of column-shaped palisade cells, which are densly packed with chloroplasts to maximise absorption of light, and therefore photosynthesis.
The spongy mesophyll contains air pockets to increase diffusion in gas exchange and photosynthesis.
The lower epidermis contains stomata and guard cells which control photosynthesis by opening during the day, and closing at night to minimise water loss through evapotranspiration.
The lower wax cuticle provides protection to the underside of the leaf.

Plants don't just need glucose, though. They require mineral ions, which they can absorb from the soil using active transport and diffusion.

A variety of different experiments can be done to test different parts of a flowering plant's nutrition.

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)

Experiment 6: Mineral ions
Place cuttings of the same plant into different mineral ion solutions: One with a complete ion solution, each of the others missing one ion and one containing just water. Place them together in controlled conditions (light, temp, etc.), then after a week or two check the plants to see any changes.

Humans

Humans gain nutrients from eating food, which has to pass through the digestive tract.
The essential nutrients are:

These are represented in the correct proportions by the eatwell plate:

This gives a good indication of what proportions of food we should be eating, but the total energy intake varies from person to person. Generally, you need more energy if:

• You have more body mass
• You are a man
• You are pregnant
• You are active
• You are a teen. After puberty, energy requirements gradually decrease, and children require less energy than adults. 

Below is a diagram of the digestive system. This is the system within your body where food is digested and nutrients absorbed. But how does this work?

1. First, food is ingested through the mouth.

It is mechanically digested, by chewing, and chemically digested, by salivary amylase. 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.
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: waves of contraction and relaxation of circular and longitudinal muscles. Peristalsis pushes the bolus of food into the stomach.

2. 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.

3. 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.

4. The ileum is where absorption 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. After being absorbed, a process called assimilation takes place, where the nutrients are used or stored by the body. 

The above diagram is of two villi. 

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.

5. 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.
The table below shows the most important digestive enzymes to know in this course:

Experiments can be done to determine the energy content of foods:

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)

Section 2 e) Key words

Absorption: When digested nutrients are absorbed from the digestive tract into the blood stream, lymphatic system, etc. through the villi.

Amylase: An enzyme that specifically targets starch and glycogen to turn it into simple sugars.

Assimilation: When nutrients absorbed by the body become part of it (used by cells, stored, etc.)

Bile: A substance created in the liver, stored in the gall bladder and released into the duodenum that neutralises the stomach contents and emulsifies lipids.

Bolus: A ball of food that is coated in saliva to make it easy to swallow

Carbohydrase: A group of enzymes that break down carbohydrates into simple sugars.

Carbohydrate: An organic compound made of carbon, hydrogen and oxygen that can be broken down into simple sugars. e.g. starch, glycogen, cellulose and sugar.

Digestion: The process of breaking down food into nutrients through the digestive system. 

Egestion: The removal of undigested and waste materials from the digestive tract.

Enzyme: A biological molecule made of amino acids that has an active site which allows it to speed up chemical reactions in the body. 

Ingestion: Taking food into the body, eating.

Lacteal: A lymph vessel found in villi. Absorbs fatty acids and glycerol.

Lipase: A group of enzymes that break down lipids into fatty acids and glycerol. 

Micro-villi: Tiny folds on the surface of the villus that increase surface area for diffusion

Oesophagus: The food pipe, where chewed-up food is swallowed. 

Pancreas: An organ that secretes digestive enzymes into the duodenum.

Peristalsis: A process in which food is moved through the digestive tract through the relaxation and contraction of circular and longitudinal muscles, creating wave-like movements that push the food forward.

Photosynthesis: The process by which plants turn carbon dioxide, sunlight and water into glucose and oxygen. This is done in the chloroplasts of the cell, where chlorophyll is contained.

Protease: A group of enzymes that break down proteins into amino acids.

Villi: Structures found in the wall of the small intestine. They are hair-like folds that increase surface area for absorption. 

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)