Biology IGCSE (Paper 1 ONLY)

Characteristics of living organisms

Movement

Respiration

Sensitivity

Control

Growth

Reproduction

Excretion

Nutrition

Characteristics of living organisms mnemonic

MRS C GREN

Movement

Organisms move towards water + food, move away from predators + poison
Even plants move a bit

Respiration

Release energy from food

Sensitivity

React to changes to environment

Control

Control internal conditions, including temp + water content

Growth

Grow and develop into adult form

Reproduction

Produce offspring for their species to survive

Excretion

Removal of waste products such as carbon dioxide + urine

Nutrition

Need nutrients to provide energy + raw materials for growth and repair
Nutrients include proteins, fats, carbohydrates

Eukaryotic

Cells contain nucleus surrounded by membrane and other organelles

Prokaryotic

No nucleus, mitochondria or chloroplasts

Plants

• Eukarotic

• Multicellular

• Contain chloroplasts + carry out PSN

• Cellulose cell wall

• Store carbohydrates as sucrose or starch

  e.g. Flowering plants: cereals (maize), herbaceous legumes (peas, beans)

Animals

• Eukaryotic

• Multicellular

• No chloroplasts so no PSN

• No cell wall so cells can change shape (important for movement)

• Most have some kind of nervous coordination, so can rapidly respond to changes in environment

• Move around from one place to another

• Store carbohydrate in cells as glycogen

  e.g. Mammals (humans), insects (houseflies, mosquitoes)

Fungi

• Eukaryotic

• Some unicellular

• Others have body called mycelium, made up of hyphae (thread-like structures), which contain lots of nuclei

• Can’t do PSN

• Cell wall made of chitin

• Most feed by saprotrophic nutrition - secrete extracellular enzymes into area outside their body to dissolve food so they can absorb nutrients

• Store carbohydrates as glycogen

  e.g. Yeast (single-celled), Mucor (multicellular, has mycelium + hyphae)

Protoctists

• Eukaryotic

• Most are single-celled

• Some look like animal cells, protozoa

• Others are more like plants - have chloroplasts so carry out PSN, e.g. algae

• Most algae are unicellular, but some are multicellular e.g. seaweed

• Some protoctists are agents of disease, e.g. Plasmodium, causing malaria

  e.g. Chlorella (plant cell-like), Amoeba (animal cell-like, lives in pond water)

Bacteria

• Prokaryotic

• Unicellular

• Cell wall, protecting bacterium + keeping shape of cell

• Cell wall made of peptidoglycan (complex compound of sugars + proteins)

• No nucleus so DNA is loose in cytoplasm

• Some can swim using flagella

• Most contain plasmids, small circular rings of DNA

• Some can do PSN

• Most feed off other organisms, living and dead

  e.g. Lactobacillus bulgaricus (can be used to make milk go sour + turn into yoghurt, rod-shaped), Pneumococcus (spherical shape)

Viruses

• Particles rather than cells, smaller than bacteria

• Can only reproduce inside living cells - depends on another organism to grow + reproduce

• Infect all types of organism

• Many shapes + sizes

• No cellular structure - have protein coat around genetic material (either DNA or RNA)

  e.g. Influenza, HIV, Tobacco mosaic (makes plant leaves discoloured by stopping them from producing chloroplasts)

Pathogen

Disease-causing organisms, including some fungi, protoctists and bacteria

Viruses are also pathogens (although not living)

e.g.
Protoctist: Plasmodium, causes malaria
Bacterium: Pneumococcus, causes pneumonia
Viruses: Influenza, causes ‘flu’, HIV, causes AIDS, Tobacco mosaic virus, causes leaf discolouration in plants by preventing formation of chloroplasts

Organelle

compartment within a cell that has a specialised function
e.g. nucleus

Cell

basic structural unit of living organisms, can be eukaryotic or prokaryotic
e.g. root hair cell

Tissue

a collection of similar cells working together to perform a function
e.g. plants have xylem + phloem tissue

Organ

group of diff. tissues working together to perform a function
e.g. lungs in mammals, leaves in plants

Organ system

a collection of different organs that work together to perform vital functions
e.g. mammals have digestive system

Nucleus

contains genetic material that controls cell’s activities

Cytoplasm

where chemical reactions take place, contains enzymes which control these reactions

Cell membrane

controls which substances can enter or leave the cell

Mitochondria

carry out aerobic resp. to create energy for the cell

Ribosomes

make proteins

Chloroplasts (plants only)

PSN occurs here, contain chlorophyll, green substance used in PSN

Cell wall (plants only)

rigid structure made of cellulose, surrounding cell membrane, supports + strengthens cell

Vacuole (plants only)

usually large central vacuole
helps support cell - stores water + pushes against cell wall when full to create turgor pressure which keeps cell firm and upright

Carbohydrates

• Contain Carbon, Hydrogen, Oxygen

• Made from simple sugars (e.g. maltose makes starch)

• Provide energy (used for respiration)

• Found in pasta, rice, sugar

• e.g. starch, glycogen

Protein

• Contain Carbon, Hydrogen, Oxygen, Nitrogen, Sulfur

• Made of long chains of amino acids

• For growth + repair of tissues

• Found in meat, fish

Lipids (fats)

• Contain Carbon, Hydrogen, Oxygen

• Built from 3 fatty acid molecules joined to 1 glycerol molecule

• Provide energy, act as energy store, provide insulation

• Found in oily fish

Glucose food test

• Add 5 drops of Benedicts solution to 5cm³ of food

• Boil in water bath (75ᵒC) for 5 mins

Blue (no sugar) → green/yellow (trace) → orange → brick red (lots)

Starch food test

• Add drops of iodine to food

Yellow/brown ➝ blue-black

Protein food test

Mash food if not already liquid

• Add 2cm² of Biuret reagent to 2cm² of food in test tube

• Mix by gently shaking

Blue → purple

Fat food tests

• 1cm depth of ethanol + small amount of food, shake test tube then add 1cm depth of water into test tube

Cloudy white suspension = fat is present

Enzyme definition

‘Biological catalysts’ that speed up reactions

• Not used up during the reaction

• Temp, pH and conc. can affect how well the enzyme functions.

How temp affects enzyme activity

Temp increases, RoR increases because particles have more energy so more collisions with substrate.

Optimum temp = enzyme works fastest.

Temp rises above optimum, enzyme denatures

pH affects enzyme activity

Work best at optimum pH, if pH moves away (lower or higher) from the optimum, RoR slows down.

Change in pH above and below optimum breaks bonds holding enzymes together.

Practical: how enzyme activity (amylase) is affected by change in temp.

• Add 5cm³ starch solution to test tube + heat to set temp. using water beaker with Bunsen burner

• Add a drop of iodine to each of the wells of a spotting tile

• Use syringe to add 2cm³ of amylase to starch solution + mix well

• Every min, transfer a droplet of solution to a new well of iodine solution (should turn blue-black)

• Repeat transfer process until iodine solution stops turning blue-black (meaning amylase has broken down all starch)

• Record time taken for reaction to be completed

• Repeat investigation for a range of temps (from 20ᵒC to 60ᵒC)

Results: how enzyme activity (amylase) is affected by change in temp.

• Amylase is enzyme which breaks down starch

• Quicker the reaction is completed, faster the enzyme is working

• This investigation shows:

  • At optimum temp., iodine stopped turning blue-black the fastest

    • Because enzyme is working at fastest rate and has digested all starch

  • At colder temps (below optimum), iodine took longer time to stop turning blue-black

    • Because amylase enzyme is working slowly due to low kinetic energy and few collisions between amylase + starch

  • At hotter temps (above optimum) the iodine turned blue-black throughout whole investigation

    • Because amylase enzyme has become denatured so can no longer bind with starch or break it down

• Limitations:

  • Method described to control temp isn’t very precise → better to use water baths

  • Starch and amylase solutions to be used should be placed in water bath and allowed to reach temp (using thermometer) before being used

Diffusion

Net movement of particles from area of higher conc. to lower conc.

Osmosis

Net movement of water molecules across partially permeable membrane from region of higher water conc. to lower water conc.

Active transport

Movement of particles against a conc. gradient (i.e. from area of lower conc. to higher conc.) using energy released during respiration

Factors that affect diffusion

• SA:Vol ratio

• Distance

• Temp

• Conc. gradient

How SA:Vol ratio affects diffusion

Larger SA:Vol ratio = faster diffusion

Smaller cube has larger SA:Vol ratio - meaning substances move into and out of this cube faster

How distance affects diffusion

Shorter distance = faster diffusion because less time taken to travel

How temp affects diffusion

Higher temp = faster diffusion

As particles get warmer, they have more energy so move faster

How conc. gradient affects diffusion

Higher conc. gradient (bigger difference between inside and outside of cell) = faster diffusion

If there are lots more particles on one side, there are more to move across

How to investigate diffusion in non-living system

1. Make up some agar jelly with phenolphthalein (pink in alkaline and colourless in acidic) and dilute sodium hydroxide (makes jelly pink)

2. Put some dilute hydrochloric acid in beaker

3. Cut out a few cubes from jelly and put them in beaker of acid

4. If you leave cubes for a while, they eventually turn colourless as acid diffuses into agar jelly + neutralises sodium hydroxide

Practical: investigating diffusion in living system

Potato cylinders

• Cut up potato into identical cylinders

• Get beakers with diff sugar solutions in them - one should be pure water, another should be very concentrated sugar solution, and a few with concentrations in between

• Measure length of cylinders, then leave a few cylinders in each beaker for half an hour

• Take them out and measure lengths again

If cylinders have drawn water by osmosis, they’ll be longer
If water has been drawn out, they’ll have shrunk

Practical: investigating diffusion in non-living system

Visking tubing

• Fix some Visking tubing over the end of a thistle funnel, then pour some sugar solution down glass tube into thistle funnel

• Put thistle funnel into beaker of pure water - measure where sugar solution comes up to on the glass tube

• Leave apparatus overnight, then measure where solution is in glass tube

Water should be drawn through Visking tubing by osmosis, forcing the solution up the glass tube

Photosynthesis

Plants make own food using PSN, converting light energy into chemical energy

Photosynthesis equation

Carbon dioxide + Water --sunlight→ Glucose + Oxygen

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

How CO₂ conc. affects rate of PSN

• One of the raw materials needed for PSN

• Increase CO₂ conc. = increased rate of PSN up to a point, then graph flattens out, as CO₂ is no longer limiting factor

How light intensity affects rate of PSN

• Chlorophyll uses light energy to perform PSN, it can only do it as quickly as light arrives

• Increase light intensity = rate of PSN increases steadily up to a certain point

How temp. affects rate of PSN

• Affects PSN rate because affects enzymes involved

• Temp increases = PSN rate increases up to a point

• Temp too high (over ~45ᵒC) = plant’s enzymes denatured, so PSN rate rapidly decreases

Leaf adaptations for photosynthesis

• Broad leaves = large SA exposed to light

• Palisade layer has most chloroplasts, near top to get most light

• Upper epidermis = transparent, light can pass through to palisade layer

• Have network of vascular bundles (transport vessels, xylem + phloem), deliver water + other nutrients to every part of leaf + take away glucose produced by PSN; also help support leaf structure

• Waxy cuticle helps reduce water loss by evaporation

• Leaf adaptations for efficient gas exchange also make PSN more efficient
  e.g. lower surface full of stomata: little holes which let CO₂ diffuse directly into leaf

Mineral ions in plants

• Needed for growth in plants

• Magnesium - to make chlorophyll (to photosynthesise)

  • deficiency → yellow leaves

• Nitrates - to make amino acids, for cell growth

  • deficiency → stunted, older leaves turn yellow

• Phosphates - to make DNA + cell membranes, for respiration + growth

  • deficiency → poor root growth, older leaves turn purple

• Potassium - helps enzymes needed for PSN and respiration

  • deficiency → poor fruit + flower growth, discoloured leaves

Photosynthesis investigation (starch production)

• Get some Elodea pondweed

• Add some NaHCO₃ solution to give an excess of CO₂

• Place in a temp. controlled water bath at 30ᵒC

• Put an upturned measuring cylinder, full of solution of the pondweed

• From a distance of 100cm shine a 40W bulb on the Elodea and eliminate all other light sources

• Count the number of bubbles produced in 5 minutes

• Repeat at 100cm another three times

• Reduce the distance by 10cm each time from 100cm-10cm and carry out again, three times

Photosynthesis investigation (need for chlorophyll)

• Drop leaf in boiling water to kill cells and break down cell membranes

• Leave leaf in a hot ethanol boiling tube for 5-10 mins (removes chlorophyll so colour changes from iodine can be seen more clearly)

• Dip leaf in boiling water to soften

• Spread leaf on white tile and cover with iodine solution

• Green leaf - entire leaf will turn blue-black as PSN is occurring in all areas of leaf

• Can use a variegated leaf (part green, part white) to test need for chlorophyll

• White areas of leaf contain no chlorophyll - only areas containing chlorophyll stain blue-black

• Areas with no chlorophyll remain orange-brown as no PSN is occurring so no starch is stored

Photosynthesis investigation (need for light)

• Same procedure as previous can be used to test need for light

• Before starting, plant must be destarched by placing in dark cupboard for 24hrs to ensure any starch that is already present in the leaves will be used up and not affect results

• After destarching, partially cover a leaf with aluminium foil and place plant in sunlight for a day

• Leaf can be removed and tested for starch using iodine

• Area of leaf covered in foil remains orange-brown (no sunlight so no PSN) and area exposed to sunlight will turn blue-black

Photosynthesis investigation (need for CO₂)

• Destarch two plants by placing in dark for 24hrs

• Put one plant in bell jar containing a beaker of sodium hydroxide (absorb CO₂ from air)

• Place other plant in bell jar containing beaker of water (control experiment), which won’t absorb CO₂ from air

• Place both plants in bright light for several hours

• Test both plants for starch using iodine

• Leaf from plant placed near sodium hydroxide remains orange-brown (no PSN due to lack of CO₂)

• Leaf from plant placed near water turns blue-black (had all requirements for PSN)

Photosynthesis investigation (evolution of O₂)

• Take a bundle of shoots of a water plant (e.g. Elodea)

• Submerge them in water beaker underneath upturned funnel

• Fill boiling tube with water and place it over end of funnel

• As O₂ is produced, bubbles of gas will collect in boiling tube and displace water

• Show that the gas collected is O₂ by relighting glowing splint

Balanced diet

• Carbohydrates

• Protein

• Lipids

• Vitamins and minerals

• Water

• Fibre

Water

Helps break down food to absorb nutrients

Fibre

• Helps waste move smoothly through the gut

• Found in wholemeal bread, fruit

Vitamin A

• Helps improve vision, keeps skin + hair healthy

• Found in liver

• Deficiency can cause night-blindness, eye ulcers

Vitamin C

• Forms part of collagen protein, makes up skin, hair, bones

• Found in citrus fruit e.g. oranges

• Deficiency can cause scurvy (liver spots on skin, bleeding gums)

Vitamin D

• Needed for calcium absorption

• Found in eggs

• Deficiency can cause rickets (softening of child's bones leading to fractures/deformity)

Calcium

• Needed to make bones + teeth

• Found in milk, cheese

• Deficiency can cause osteoporosis

Iron

• Needed to make haemoglobin to carry O₂

• Found in red meat

• Deficiency can cause anaemia (tiredness, shortness of breath, paleness due to less O₂ reaching cells so less respiration/energy)

Why energy requirements can vary

• Activity level: more active people need more energy than sedentary people (e.g. office worker needs 10,000kJ a day, manual worker needs 15,000kJ a day)

• Age: children + teens need more energy than older people - need energy to grow + generally more active

• Pregnancy: greater mass = more energy needed + energy for baby to develop

Investigating energy content of food sample

• Need dry food that burns easily

• Weigh a small amount of food, skewer it on mounted needle

• Add a set volume of water in a test tube (held with clamp)

  • will be used to measure amount of energy released when food is burnt

• Measure water temp, then set fire to food using Bunsen flame

• Hold burning food under boiling tube until it goes out

• Relight food + hold under tube - keep doing until food doesn’t catch fire again

• Measure temp of water again

Energy equation

J per g = (temp rise x water mass) x 4.18 / mass of food (g)

Digestive system diagram

alimentary canal

the whole passage along which food passes through the body from mouth to anus. includes oesophagus, stomach, and intestines.

Mouth

• Salivary glands produce amylase enzyme in saliva

• Teeth mechanically break down food

Oesophagus

Muscular tube connecting mouth to stomach

Stomach

• Mechanically digests food by churning actions

• Produces protease enzyme, pepsin

• Produces HCl to:

  • Kill bacteria

  • Give optimum pH for protease enzyme to work (pH 2 - acidic)

Liver

Produces bile

Gall bladder

Stores bile

Pancreas

• Produces protease, amylase, lipase enzymes + releases them into small intestine

Small intestine

• Absorbs nutrients out of alimentary canal into body

• Produces protease, amylase, lipase enzymes to complete digestion

• First part: duodenum, last part: ileum

Large intestine

Absorbs excess water, salts and Vitamin K

Rectum

stores faeces to be released via anus

Bile

Produced in liver, stored in gallbladder

Bile released from gallbladder and reaches small intestine via bile duct

Functions:

• alkaline so neutralises stomach acid to provide optimum pH for enzymes in small intestine to work

• emulsifies fats (breaks them up into small droplets → larger SA for enzyme lipase to work on = faster digestion)

Peristalsis

Series of wave-like muscle contractions to push food down the gut (oesophagus + small intestine)

Protease

proteins → amino acids

produced in stomach (pepsin), pancreas (released into small intestine), small intestine

optimum pH - 2 in stomach, 7-8 in small intestine

Carbohydrase

Carbohydrates ➡ glucose

e.g. amylase + maltase

Lipase

lipids ➡ glycerol + fatty acids

produced in pancreas, small intestine

optimum pH - 8 in small intestine and pancreas

Small intestine adaptations

• Ileum (small intestine) is very long to provide large surface area for absorption of digested food

• Finger-like projections called villi (each have microvilli) to increase SA for digested food to diffuse across, giving a faster rate of diffusion

• Villi have thin walls (one cell thick) for short diffusion distance so digested food can rapidly pass through wall

• Has good blood supply, each villus with its own capillary so digested food can be rapidly absorbed + carried away by blood so diffusion gradient is maintained for efficient diffusion

• each villus has a lacteal where digested fats are absorbed

Respiration

Process of transferring energy from glucose - happens constantly in every living cell

Produces ATP which stores energy needed for many cell processes

When a cell needs energy, ATP molecules are broken down + energy is released

Aerobic respiration

• Needs oxygen

• Most efficient way to transfer energy from glucose

• Most common type of respiration used

glucose + oxygen → carbon dioxide + water (+ energy)

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Anaerobic respiration

• When you do intense exercise, body can’t supply enough O₂ to muscles for aerobic respiration so needs anaerobic respiration

• Releases less energy per glucose molecule than aerobic respiration

• Glucose only partially broken down → lactic acid also produced

• Lactic acid builds up in muscles, gets painful and leads to cramp

glucose → lactic acid (+ energy)

Anaerobic respiration in plants

• Produce ethanol + CO₂ instead of lactic acid

glucose → ethanol + carbon dioxide (+ energy)

Investigating CO₂ produced by respiring seeds

Can use hydrogen-carbonate indictor to show living organisms produce CO₂ as they respire
Solution is orange but changes to yellow in presence of CO₂

• Soak some dried beans in water for 1 day
  They will start to germinate. Germinating beans respire.

• Boil a similar-sized, second bunch of dried beans. This will kill the beans + make sure they can’t respire. Dead beans act as your control.

• Put same amount of hydrogen-carbonate indicator in 2 test tubes

• Place gauze platform in each test tube and place beans on it

• Seal test tubes with rubber bung

• Leave apparatus for set period of time (e.g. 1hr)

• During that time, CO₂ should have turned the hydrogen-carbonate indicator yellow