Section 2 f) Summary

Respiration is the chemical breakdown of sugars to release energy in living cells.
This is very important, without it we wouldn't have the energy for any of the other life processes. Notable everyday energy-requiring processes include:

• nerve impulses
• cell division
• muscle contraction
• homeostasis and thermoregulation
• protein synthesis
• active transport

Aerobic respiration is releasing energy from glucose by reacting it with oxygen:

Glucose + Oxygen --> Carbon dioxide + Water (+ Energy)

C6H12O6 + 6O2 --> 6CO2 + 6H2O (+ Energy)

Anaerobic respiration is releasing energy from glucose without oxygen. It releases different toxic by-products in plants and animals, and less energy than aerobic respiration:

Plants: Glucose --> Carbon dioxide + Ethanol (+ Some energy)

Animals: Glucose --> Carbon dioxide + Lactic acid (+ Some energy)

The rate of respiration is affected by enzymes and their optimum temperature and pH. 

We can investigate respiration through the following experiments:

Rising dough (yeast):

1. Place dough into oiled measuring cylinders, and record their height. 
2. Place each measuring cylinder into a water bath (regular intervals of 10℃), with three cylinders in each bath so an average for each can be found.
3. Measure the height of the dough every 10 minutes, for 30 minutes.
4. Record the average heights in a table, then find the average percentage change in height. 

Seeds:

1. Fill one vacuum flask with living seeds, and thee other with surface-sterilised seeds. Place a thermometer in each and seal the top with cotton wool.
2. Record starting temp, then wait 30 minutes. 
3. The flask containing the living seeds will have increased in temperature, and the one with dead seeds will not. 

Heat is a by-product of the use of the energy for respiration. 

Humans: 

You can see that we produce carbon dioxide by blowing into a straw in a boiling tube containing lime water - it goes cloudy - or hydrogen carbonate indicator - it goes from red to yellow. 

Section 2 f) Key Words

Aerobic respiration: Respiration including oxygen. Releases more energy, and has less toxic by-products.
Glucose + Oxygen --> Carbon dioxide + Water

Anaerobic respiration: Respiration without oxygen. Releases less energy than aerobic respiration, and has toxic by-products, e.g. lactic acid in animals, ethanol in plants and yeast.
Glucose --> Carbon dioxide + Lactic acid
Glucose --> Carbon dioxide + Ethanol

Respiration: The chemical breakdown of sugar molecules in living cells to release energy

Section 2 f) Specification

2.33 understand that the process of respiration releases energy in living organisms

Respiration is the process by which living organisms release energy from sugar.

2.34 describe the differences between aerobic and anaerobic respiration

Aerobic respiration is respiration that occurs with oxygen, and anaerobic is without. Anaerobic respiration produces significantly less energy than aerobic respiration, and usually has a toxic by-product (lactic acid in humans, alcohol in yeast or plants, etc.)

2.35 write the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms

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

2.36 write the word equation for anaerobic respiration in plants and in animals

Plants: Glucose --> Carbon dioxide + Ethanol (+some energy)
Animals: Glucose --> Carbon dioxide + Lactic acid (+some energy)

2.37 describe experiments to investigate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms.

Rising dough (yeast):

1. Place dough into oiled measuring cylinders, and record their height. 
2. Place each measuring cylinder into a water bath (regular intervals of 10℃), with three cylinders in each bath so an average for each can be found.
3. Measure the height of the dough every 10 minutes, for 30 minutes.
4. Record the average heights in a table, then find the average percentage change in height. 

Seeds:

1. Fill one vacuum flask with living seeds, and thee other with surface-sterilised seeds. Place a thermometer in each and seal the top with cotton wool.
2. Record starting temp, then wait 30 minutes. 
3. The flask containing the living seeds will have increased in temperature, and the one with dead seeds will not. 

Heat is a by-product of the use of the energy for respiration. 

Humans: 

You can see that we produce carbon dioxide by blowing into a straw in a boiling tube containing lime water - it goes cloudy - or hydrogen carbonate indicator - it goes from red to yellow. 

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)

Section 2 d) Summary

There are three ways in which substances can move into and out of cells:

• Diffusion
• Osmosis
• Active transport

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration. This can happen in any fluid, and at the end the substance will be evenly dispersed. It is a passive process, meaning it happens in the direction of the concentration gradient and therefore doesn't require any energy. 

Examples include gas exchange in the lungs, gas exchange in the leaf, and assimilation in the small intestine. 

Experiments:
Diffusion can be investigated by placing food colouring or potassium permangenate into water. Then by timing how long it takes for the water to become entirely one colour at different temperatures will tell us how temperature affects diffusion.

Factors affecting the rate of diffusion include

• Distance: Shorter distances mean faster diffusion
• Temperature: Higher temperatures mean more kinetic energy, and faster moving particles
• Surface area: Larger surface area means faster diffusion
• Size of particles: Smaller particles move more quickly
• Concentration gradient: Steeper concentration gradients mean faster diffusion
• Pressure (in gas): This is the same principle as concentration, there is more particles in a smaller volume of space 

Osmosis is the net movement of water particles across a semi-permeable membrane from an area of high water potential to an area of low water potential. 

Examples of this include plants using root hair cells to take in water from the soil, water moving around plant cells for evenly distributed turgidity, which supports the plant. 

Osmosis is relatively similar to diffusion, the difference being osmosis is in reference only to the movement of water particles across a semi-permeable membrane. 

Experiments:

Osmosis can be investigated using Visking tubing, sugar solution and water. (Model cell)
1. Place sugar solution in one sealed Visking tube, and water in another. Weigh each.
2. Place the sugar tube in a beaker full of water, and the water tube in a beaker full of sugar solution.
3. Remove the tubes after 30 minutes and weigh again. Note the changes.
You can see that the sugar tube has increased in mass, because osmosis has caused water to enter the tube. The water tube has lost mass, as osmosis has caused water to leave the Visking tubing.

Osmosis can also be investigated using potato cylinders.
1. Using a cork borer, create a potato cylinder and cut into equal lengths of 3cm.
2. Weigh each cylinder, then place each into different concentrations of sugar solution, making sure to keep track of which is which.
3. After 30 minutes, remove and dry the potato cylinders, then reweigh and note the change in mass for each of them. ( percentage change in mass = (final mass - initial mass) x 100 / initial mass )
These results can be graphed to find the water potential of the potato, as this is the point at which the mass should not change.

Active transport is the movement of particles against a concentration gradient, from an area of low concentration to an area of high concentration. It is an active process; it requires energy from respiration, unlike diffusion and osmosis. 

Examples include reabsorption of glucose in the nephron and root hair cells in a plant taking in mineral ions.

Section 2 d) Key Words

Active transport: Movement against a concentration gradient

Concentration: How many particles of a substance there are in a certain volume.

Diffusion: The net movement of particles from an area of high concentration to an area of low concentration

Osmosis: The net movement of water particles across a semi-permeable membrane from an area of high water potential to an area of low water potential

Semi-permeable membrane: A membrane that allows some particles through, but not all

Water potential: The concentration of water particles, or how dilute a solution is

Section 2 d) Specification

2.12 understand definitions of diffusion, osmosis and active transport

Diffusion: The net movement of particles from an area of high concentration to an area of low concentration in a fluid. Goes with the concentration gradient (passive), so doesn't require energy.

Osmosis: The net movement of water particles through a semi-permeable membrane from an area of high water potential to an area of low water potential, (an area with higher concentration of water particles to an area of low concentration of water particles) Goes with the concentration gradient (passive), so doesn't require energy.

Active Transport: The movement of particles from an area of low concentration to an area of high concentration, absorption against a concentration gradient. Requires energy from respiration.

2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

Diffusion: gas exchange in the alveoli

Osmosis: Water moves around plant cells, making them turgid for support

Active transport: Root hair cells absorb mineral ions from the soil

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

Plants don't have bones or an exoskeleton, so their means of support is turgid cells, which, with their cellulose cell walls, are strong and support the plant's shape. Without turgidity, the plant wilts and dies.

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

Diffusion and osmosis are affected by the following factors:

• Temperature. The particles move more quickly as they have more kinetic energy with increased temperature, meaning they move along the concentration gradient more quickly. 
• Concentration gradient. A greater difference in concentration means a steeper concentration gradient. (Fick's Law)
• Distance. Further distances mean slower diffusion, for obvious reasons. It takes longer for particles to travel a further distance. 
• Particle size. Larger particles in diffusion are heavier, and therefore move more slowly.
• Surface area to volume ratio. If the surface area is proportionally larger, there is more surface for passive transport to occur through. 

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

Osmosis can be investigated using Visking tubing, sugar solution and water. (Model cell)
1. Place sugar solution in one sealed Visking tube, and water in another. Weigh each.
2. Place the sugar tube in a beaker full of water, and the water tube in a beaker full of sugar solution.
3. Remove the tubes after 30 minutes and weigh again. Note the changes.
You can see that the sugar tube has increased in mass, because osmosis has caused water to enter the tube. The water tube has lost mass, as osmosis has caused water to leave the Visking tubing.

Osmosis can also be investigated using potato cylinders.
1. Using a cork borer, create a potato cylinder and cut into equal lengths of 3cm.
2. Weigh each cylinder, then place each into different concentrations of sugar solution, making sure to keep track of which is which.
3. After 30 minutes, remove and dry the potato cylinders, then reweigh and note the change in mass for each of them. ( percentage change in mass = (final mass - initial mass) x 100 / initial mass )
These results can be graphed to find the water potential of the potato, as this is the point at which the mass should not change.

Diffusion can be investigated by placing food colouring into water. Then by timing how long it takes for the water to become entirely one colour at different temperatures will tell us how temperature affects diffusion.

Section 2 c) Summary

Proteins are long chains of amino acids. Made up of carbon, hydrogen, oxygen and nitrogen: CHON

Carbohydrates are long chains of simple sugars. Made up of carbon, hydrogen and oxygen: CHO

Lipids are made of glycerol and three fatty acids. Made up of carbon, hydrogen and oxygen: CHO

Enzymes are biological catalysts, they're specialized proteins that speed up biological reactions, such as digestion, without becoming chemically involved. They are adapted to work in ideal conditions depending on where they should be, for example human enzymes work at an optimum temperature of around 37 ℃, because this is average body temperature.
Protease in the stomach, and enzyme that breaks down proteins into amino acids, works at an optimum pH of 2, which is the acidity of the hydrochloric acid found in the stomach, however salivary amylase, found in the mouth, is denatured in these conditions as the mouth is much less acidic.
An enzyme will become denatured in extremes of pH, as well as high temperatures. Low temperatures will not denature the enzyme, but will slow it so it isn't able to work efficiently.

These two graphs depict enzyme activity based on temperature and pH:

Optimum temperature of enzymes can be found by completing the following experiment:

1. Mixing amylase (protein that breaks down carbohydrates into glucose) with starch in test tubes, and placing them in water baths of varying temperatures (should be regular intervals).
2. Testing samples for starch with iodine every 30 seconds
3. Record how long it takes for the iodine to test negative for starch, this is when the amylase has broken down all or most of the starch.

Graph the results to determine the optimum temperature.

Iodine is an orange-brown colour, but turns black-blue when exposed to starch. This is how we test for starch.

Benedict's solution is blue in colour, but when heated with a simple sugar such as glucose, it turns red. This is how we test for glucose.

Section 2 c) Key Words

Active site: The part of the enzyme that catalyses the reaction, the 'key' part of the lock and key model.

Amino acid: The monomer of a protein. A molecule made up of carbon, hydrogen, oxygen and nitrogen that bonds with other amino acids to form proteins.

Carbohydrates: Long chain molecules (polymers) made up of monosaccharides, e.g. starch or glycogen

Denatured: When the active site of an enzyme is changed

Disaccharide: Made up of two monosaccharides. e.g. sucrose

Enzyme: A biological catalyst. It is a type of protein that has an 'active site' that it uses to break down substrates into products, or bind them together. e.g. amylase, protease

Fatty acid: Three of these bind with a molecule of glycerol to form a lipid. Made of carbon, hydrogen and oxygen.

Glucose: A monosaccharide that makes up carbohydrates such as starch or glycogen.

Glycerol: One of the building blocks of a lipid. Attaches to three fatty acids.

Glycogen: A carbohydrate that animals make to store glucose. A polymer.

Lipid: Oil or fats, made up of glycerol and three fatty acids (Each made of carbon, hydrogen and oxygen: CHO)

Monomer: A single unit, simple molecule. Many of these bind together to form a long-chain polymer.

Monosaccharide: A simple, single sugar, e.g. glucose

Polymer: A long-chain molecule made up of lots of monomers bound together

Polysaccharide: A complex sugar made up of lots of monosaccharides.

Protein: Polymer of amino acids. Organic chain of molecules.

Starch: Storage of carbohydrates in plants, long-chain molecule of glucose.

Substrate: The 'reactants' in an enzyme-aided reaction.

Section 2 c) Specfication

2.5 identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)

In carbohydrates and lipids, there are CHO: Carbon, Hydrogen and Oxygen.
In proteins, there are CHON: Carbon, Hydrogen, Oxygen and Nitrogen.

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol

Starch and glycogen are carbohydrates that are polymers, their monomers being simple sugars (monosaccharides) such as glucose: C6H12O6

Proteins are made of amino acids, which join together to form unique shapes and combinations, important for each protein to have its own properties.

Lipids are made up of fatty acids and glycerol, in this structure:

2.7 describe the tests for glucose and starch

Starch: Test using iodine solution. If it changes from brown-orange to blue-black, there is starch present.

Glucose: heat with Benedict's solution. It will turn red if positive.

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

Enzymes work with the lock and key model. They are a certain shape that allows substrates to fit in, then bond together or break apart in the active site. It speeds up the reaction. They are useful in digestion, enzymes such as protease break up proteins, amylase breaks up starch into glucose,

2.9 understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site

The active site of the enzyme is the most important part of it. It allows the enzyme to take part in metabolic reactions, however if it is put in conditions that are too far from the optimum it can be damaged. In high temperatures, the shape of the active site can be changed, rendering the enzyme useless. The enzyme is denatured.

This curve depicts the way temperature affects enzymes:

Beyond the optimum temperature, the enzyme is denatured. Leading up to the optimum temperature, the enzyme activity increases due to increasing kinetic energy of the particles which increases the rate of collisions.

2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

Extreme change in pH can also cause the enzyme to be denatured. This varies depending on the optimum pH of the enzyme, but a very extreme pH will denature any enzyme. 

2.11 describe experiments to investigate how enzyme activity can be affected by changes in temperature.

1. Place test tubes containing the same mixture of amylase and starch in water baths of different temperatures with regular temperature intervals (e.g. 20℃, 30℃, 40℃, 50℃, 60℃, 70℃)
2. Take a sample from each at regular time intervals (every 30 seconds) and test for starch with iodine
3. Record which sample was the first to not test positive for starch.
From this, you can see how long it took for the enzyme to break down the starch. It can be graphed to determine the optimum temperature.