2.5Structures and Functions in Living Organisms
Nutrition — Edexcel Modular - OL Revision Notes & Topical Questions
20 min read 30 parts Lesson 5 of 12 2 quizzes
Nutrition Edexcel O Level Modular Biology notes: understand the process of photosynthesis and its importance in the conversion of light energy to chemical energyStomach acid kills microbes and gives pepsin its optimum pH.Villi have thin walls, capillaries and lacteals.Large intes…
- Nutrition Edexcel O Level Modular Biology: what to do next
- Mechanical digestion
- Chemical digestion
- Give / State / Name
- Evaluate / Assess
- Keywords the mark scheme looks for in this lesson
Section 1 of 30Process & sequence
- Mouth
- Oesophagus (peristalsis)
- Stomach
- Small intestine (absorption)
- Large intestine (water)
- Rectum, anus
Section 2 of 30Keep going
Nutrition Edexcel O Level Modular Biology: what to do next
These Nutrition Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your Nutrition Edexcel O Level Modular Biology understanding with the practice questions below, then reread any Nutrition Edexcel O Level Modular Biology point you were unsure about before moving on.
Section 3 of 30Leaf adaptations for photosynthesis
The leaf is adapted to absorb light and carbon dioxide.
Section 4 of 30Plants make more than carbohydrates
Photosynthesis provides carbohydrates, but plants also require proteins, lipids and nucleic acids (DNA).
| Deficiency | Symptom | Reason |
|---|---|---|
| Nitrate | Stunted growth, older leaves yellow | Cannot make enough amino acids and proteins |
| Magnesium | Leaves yellow (chlorosis), especially between veins | Cannot make chlorophyll |
Section 5 of 30Practical: oxygen produced by pondweed
As photosynthesis occurs, oxygen gas produced is released as bubbles from the cut end. More bubbles mean a faster rate. A heat shield (water between the lamp and plant) prevents temperature changes. Rate falls as the lamp moves away because light intensity falls (inverse square relationship).
Section 6 of 30Why leaves are tested for starch rather than glucose
Although plants synthesise glucose, the glucose is quickly used up, converted into other substances and transported or stored as starch. Starch is stored in the chloroplasts where photosynthesis occurs, so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.
Section 7 of 30Photosynthesis, respiration and gas exchange in leaves
During the day a plant photosynthesises faster than it respires, so there is a net uptake of carbon dioxide and a net release of oxygen.
- which is red at atmospheric carbon dioxide level, yellow when carbon dioxide is high and purple when low (photosynthesis exceeds respiration).
- (respiration only)
| Tube conditions | Indicator colour | Explanation |
|---|---|---|
| Leaf in dark (foil-wrapped) | Yellow | Only respiration, so carbon dioxide builds up |
| Leaf in bright light | Purple | Photosynthesis uses more carbon dioxide than is produced |
| Leaf in moderate light | Red | Rates balanced |
Uses of photosynthetic products and importance: photosynthesis is the source of food energy for almost all food chains, and the source of the oxygen in the atmosphere.
Section 8 of 30Compare
| Enzyme | Made in | Acts in | Substrate | Product | Optimum pH |
|---|---|---|---|---|---|
| Salivary amylase | Salivary glands | Mouth | Starch | Maltose | 7 |
| Pepsin | Stomach | Stomach | Protein | Peptides | 2 |
| Pancreatic amylase | Pancreas | Small intestine | Starch | Maltose | 8 |
| Trypsin | Pancreas | Small intestine | Protein | Peptides | 8 |
| Lipase | Pancreas | Small intestine | Lipids | Fatty acids + glycerol | 8 |
| Maltase | Small intestine wall | Small intestine | Maltose | Glucose | 8 |
Section 9 of 30Worked examples
Explain how the palisade layer is adapted for photosynthesis. [2]2 marks
It is at the top, so absorbs most light, and its cells are packed with chloroplasts.
Explain why magnesium deficiency makes leaves yellow. [2]2 marks
Magnesium is needed to make chlorophyll; without it, the leaves have less of the green pigment.
Describe how to measure the rate of photosynthesis using pondweed. [3]3 marks
Count bubbles of oxygen per minute from the cut end at set light intensities, keeping temperature and carbon dioxide constant.
Why test for starch instead of glucose? [1]1 mark
Glucose is rapidly converted to starch and other substances.
Section 10 of 30Investigating the need for light
- Ethanol is flammable, so turn off the Bunsen burner;
- use an electric water bath or water from a just-boiled kettle.
Result
- the area exposed to light turns blue-black (starch present);
- the covered area stays yellow-brown (no starch), so light is necessary for photosynthesis.
Section 11 of 30Investigating the need for carbon dioxide
After de-starching, enclose one leaf in a conical flask containing potassium hydroxide (which absorbs carbon dioxide) and another leaf in a control flask without it, then leave in light.
- as it could not photosynthesise; the control leaf turns blue-black.
Section 12 of 30Balanced diet and malnutrition
A balanced diet consists of all the food groups in the correct proportions. An unbalanced diet can lead to malnutrition, which causes health problems such as obesity (too much energy), kwashiorkor (too little protein), scurvy (vitamin C), rickets (vitamin D or calcium) and anaemia (iron).
| Nutrient | Sources | Function |
|---|---|---|
| Carbohydrate | Bread, cereals, pasta, rice, potatoes | Energy |
| Protein | Meat, fish, dairy, pulses | Growth and repair |
| Lipid | Oils, butter | Energy store, insulation |
| Fibre | Vegetables, wholegrain | Provides bulk (roughage) to push food through the intestine |
| Vitamins and minerals | Fruit, vegetables, meat, dairy | Needed in small quantities to maintain health |
Dietary needs vary
- more active people need more energy;
- children need a higher proportion of protein for growth;
- pregnant women need extra energy, calcium and iron to support the fetus.
Section 13 of 30Nutritional data: energy requirements and disorders
Energy requirements depend on age, sex, activity and size.
| Disorder | Cause | Symptoms |
|---|---|---|
| Scurvy | Lack of vitamin C | Bleeding gums, slow healing |
| Rickets | Lack of vitamin D or calcium | Soft, bowed bones in children |
| Anaemia | Lack of iron | Pale, tired, short of breath |
| Kwashiorkor | Lack of protein | Swollen abdomen, poor growth |
Tests for food types
- Benedict's for reducing sugars, iodine for starch, biuret for protein and ethanol emulsion for lipids;
- DCPIP for vitamin C, which is decolourised faster by foods with more vitamin C.
Section 14 of 30Worked examples
Describe why a leaf is boiled in ethanol. [2]2 marks
To remove chlorophyll so the iodine colour change is visible.
Explain why the covered part of a leaf stays yellow-brown. [2]2 marks
It received no light, so photosynthesis could not occur and no starch was made.
Why do children need more protein per kilogram than adults? [1]1 mark
For growth.
Suggest why a plant is de-starched. [1]1 mark
To make sure any starch found was made during the experiment.
Section 15 of 30Organs of the alimentary canal
The digestive system is an organ system. Digestion breaks large insoluble molecules such as starch and proteins into smaller soluble ones that can be absorbed into the blood and delivered to cells. The alimentary canal and accessory organs work together.
| Organ | Role |
|---|---|
| Mouth and salivary glands | Teeth chew food (mechanical digestion, increasing surface area); salivary amylase starts starch digestion |
| Oesophagus | Peristalsis pushes the bolus to the stomach |
| Stomach | Churning; pepsin (protease); hydrochloric acid kills bacteria and gives low pH |
| Liver and gall bladder | Make and store bile |
| Pancreas | Makes digestive enzymes and the hormone insulin; food does not pass through it |
| Small intestine (duodenum, ileum) | Digestion completed; absorption; pH 8-9 |
| Large intestine | Absorbs water; forms faeces |
Section 16 of 30Peristalsis and chemical digestion
Peristalsis is a wave of contraction of circular and longitudinal muscles in the gut wall that pushes food along. Once in the stomach the food is churned into chyme. Mechanical digestion (chewing, churning, emulsification) breaks food into smaller pieces and increases surface area. Chemical digestion mainly takes place by enzymes, which break bonds in large molecules.
Section 17 of 30Bile
Bile is an alkaline fluid produced by the liver and stored in the gall bladder.
- giving the alkaline pH needed for pancreatic enzymes, and (2) emulsifies lipids, breaking large drops into smaller ones with a larger surface area,
- so lipase can digest them faster.
Section 18 of 30Small intestine: structure and adaptations
Absorption is the movement of small digested molecules from the gut into the blood (glucose and amino acids) and lymph (fatty acids and glycerol).
- and microvilli on the cells.
Section 19 of 30Tests, adaptations and extended-answer structure
For a six-mark question describing digestion, structure your answer along the gut: mouth (amylase, chewing), stomach (pepsin, acid), small intestine (bile, lipase, amylase, protease, maltase, absorption), large intestine (water absorption).
- and the digestion is done by lipase.
Surface area calculations
- if a villus is modelled as a cylinder of radius 0.1 mm and height 1 mm, its curved surface area is 2 x pi x 0.1 x 1 = 0.63 mm2;
- with millions of villi the total absorbing area is hundreds of times that of a smooth tube.
- so lactose passes undigested to the large intestine where bacteria ferment it, causing gas and diarrhoea.
Section 20 of 30Worked examples
Name the enzymes that digest starch to glucose. [2]2 marks
Amylase (to maltose) and maltase (to glucose).
State two functions of bile. [2]2 marks
Neutralises acid from the stomach; emulsifies fats.
Explain why emulsification speeds up fat digestion. [2]2 marks
It breaks large droplets into smaller ones, increasing surface area for lipase.
Describe peristalsis. [2]2 marks
Waves of muscle contraction in the gut wall by circular and longitudinal muscles push food along.
Section 21 of 30The principle
Food stores chemical energy. When it is burned, this energy is transferred as heat to surrounding water. The larger the increase in water temperature, the more energy was stored in the food. A food sample burned under a boiling tube of water is a simple calorimeter.
Section 22 of 30Method
Section 23 of 30Calculating energy
Section 24 of 30Evaluation
| Problem | Effect | Improvement |
|---|---|---|
| Heat lost to the air | Results too low | Use a draught shield, insulate the tube, keep the food close |
| Incomplete combustion | Less energy transferred | Relight the sample until it will not burn |
| Different starting temperatures | Unfair comparison | Start each test at the same temperature |
| Small mass of food | Large percentage errors | Use a larger mass and repeat |
Compare foods using energy per gram. Fats give about 37 kJ/g, carbohydrates and proteins about 17 kJ/g, so high-fat foods give the highest values. Variables to control: volume of water, distance between flame and tube, mass of food.
Section 25 of 30Planning the practical with CORMS
C - changethe type of food (peanut, crisps, bread, cheese).
Accuracy and precisionthe mean energy value from this method is always lower than the value on the packet because heat is lost.
- For example, a peanut at 24 kJ/g contains much more energy than bread at 10 kJ/g, because it contains more fat.
Section 26 of 30Worked examples
Calculate the energy transferred when 25 g water rises by 16 C. [2]2 marks
25 x 16 x 4.2 = 1680 J.
0.8 g of crisps heat 25 g of water by 10 C. Calculate energy per gram. [3]3 marks
Energy = 25 x 10 x 4.2 = 1050 J; per gram = 1050 / 0.8 = 1310 J/g.
Give two reasons why the result is lower than the true value. [2]2 marks
Heat is lost to the surroundings; the food may not burn completely.
Section 27 of 30Key terms
| Term | Meaning |
|---|---|
| Palisade layer | Leaf layer with many chloroplasts at the top. |
| Spongy mesophyll | Leaf layer with air spaces. |
| Chlorosis | Yellowing of leaves. |
| Nitrate | Mineral ion needed for amino acids. |
| Magnesium | Mineral ion needed for chlorophyll. |
| Term | Meaning |
|---|---|
| De-starch | Remove starch from leaves by keeping a plant in the dark. |
| Potassium hydroxide | A chemical that absorbs carbon dioxide. |
| Balanced diet | A diet containing all nutrients in correct proportions. |
| Malnutrition | Poor health from an unbalanced diet. |
| Fibre | Indigestible plant material giving bulk. |
| Term | Meaning |
|---|---|
| Peristalsis | Muscular waves moving food along the gut. |
| Chyme | Semi-liquid mixture of food and stomach secretions. |
| Bile | Alkaline fluid from the liver that emulsifies fat. |
| Villi | Finger-like projections increasing absorption area. |
| Pepsin | Protease from the stomach. |
| Lipase | Enzyme that digests fats. |
| Term | Meaning |
|---|---|
| Calorimetry | Measuring energy transfers, e.g. from burning food. |
| Specific heat capacity of water | 4.2 J/g/C. |
| Combustion | Burning. |
| Draught shield | A screen used to reduce heat loss. |
Section 28 of 30Syllabus checklist
Section 29 of 30Command terms
Section 30 of 30Exam technique
Marked practiceQuizzes for this lesson
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