Food production and preservation

Bread-making uses yeast fungi. When the yeast is provided with sugars, fermentation occurs, breaking down sugar to produce carbon dioxide. The release of CO2 makes the bread rise and results in the holes found in bread. Alcohol is also produced during fermentation, but evaporates when bread is cooked.

Lactic acid bacteria are used in a number of methods of food production, including cheese making (lactococcus) and yogurt (lactobacillus). Cheese making involves the acidification, coagulation, dehydration and salting. During acidification the lactic acid bacteria are added to milk as a starter culture. The lactic acid they produce give cheese an acidic flavour and coagulate casein protein. The bacteria also release enzymes that ripen cheese and produce antibacterial substances that slow growth of pathogens allowing longer storage.

In yogurt production the lactic acid lowers pH of milk to 4, gives yogurt its tangy taste, changes texture of milk and inhibits spoilage allowing longer storage.

When food spoils, it becomes hard to eat because of the change in texture, colour, smell or taste. These changes occur because of the effect of enzymes on carbohydrates, proteins and fats. Preserving methods avoid this eg in jam fruit is boiled in a sugar until water has evaporated and jam is set in gel. boiling kills all the micro-organisms in on the fruit and sealing in jam stops spoilage by micro-organisms. However high moisture means mould can grow when jam is opened.

All methods of food preservation are made to produce an environment free of micro-organisms or one that makes them unable to grow and reproduce examples:
Refrigeration - temperature below 4 degrees slow growth of micro-organism eg milk
Freezing - temperature even lower than fridge increases storage time by stopping growth and reproduction eg meat
Salting- salt removes water from bacteria and fungi, stops growth eg bacon
acidificaton- lactic acid lowers PH slows growth of spoilage micro-organisms eg yogurt
drying - remove water to stops growth eg garlic
freeze-drying freezing, removal of water and sealing increases storage time
canning - cooking kills micro-organisms and sealing prevents them entering again eg peaches
heating denatures the enzymes and proteins in cell membrane so cells cant carry out life processes like respiration, digestion and reproduction. The sealed can and lid stops oxygen from entering food, stopping respiration, so they are unable to produce energy.
If can is opened, micro-organisms can enter food again, growing reproducing and making toxins that make food unsafe to eat. oxygen in the air enable aerobic micro-organisms to carry out respiration. Putting can in the fridge can slow growth and reproduction as the cold slows chemical reactions.

Sewage treatment
sewage is wastewater and solid material from bathroom, toilet, kitchen, laundries, and industrial wastewater. The feeding and respiration of micro-organisms breaks down the organic material in sewage. Liquid and solid parts of sewage are separated - aerobic bacteria feed on the liquid part of sewage, breaking it down to release nutrients. Anaerobic bacteria, which produce methane gas, break down the solid parts of sewage.
Bacteria in the aeration tank are saprotrophs that decompose organic material in sewage, breaking it into carbon dioxide, water, nutrients and minerals that can be used by bacteria and plants. First bacteria carry our extracellular digestion and some of the digested material is used for respiration to make energy needed for growth and reproduction. Oxygen is added to tanks to ensure aerobic bacteria can carry out aerobic respiration and remain active.

Sewage treatment is important as it removes pathogenic micro-organisms and organic material so the liquid can be released into waterways and not cause disease or nutrient overloading.

producing antibiotics
penicillin was the first antibiotic produced and used to treat bacterial infections. It is now produced in large amounts by fermentation from mould or synthetically.

Antibiotics upset the reproduction, feeding, growth and metabolism of bacterial cells. different antibiotics affect different life processes. For example antibiotic that damages DNA stops protein being made and so stops growth and reproduction of bacterium.

diagram:

Antibiotics work by upsetting the function of cells like bacteria and fungi eg damage cell membrane. Antibiotics don't work against viruses as they are not cells, do not have parts like cell membranes and do not carry out most life processes eg respiration
Vaccine delivery
A vaccine can be injected to give an organism immunity to a disease. research is being done to develop vaccine delivery systems using lactococcus bacteria. The bacteria is genetically modified so it has protein on its surface that are the same as those carried on a pathogenic species eg lactococcus can be modified to produce proteins the same as streptococcus that causes strep throat. When the modified lactococcus is sprayed into the nose, it causes an immune response to the pathogens proteins, which gives future immunity to streptococcus

Genetic mutation in epidemiology
epidemiology is the study of patterns of disease. Patterns of disease have been studied through the identification of mutations in genes carried by micro-organisms. For example, investigation of mutations in the bacteria Bacillus anthracis (anthrax) has allowed specific strains of the pathogen to be identified and this information used in epidemiology. eg a anthrax outbreak in South africa was shown to caused by a rare strain of anthrax found in soil. In another case, a death by anthrax was found to be from a laboratory strain and was found to be murder.

In epidemiology of breast and other cancers, genetically modified (GM) bacteria are used to study the effect of genetic mutation in different genes  eg tumour suppressor genes. Different mutations cause different changes in the protein produced as a result of the gene. Using GM bacteria lets researchers investigate the specific change that different mutations have on the resulting protein and consider the effect this has on a person with the mutation.

Harmful effects on micro-organisms
food poisoning
disease
microbial attack on material
antibiotic resistance

Food poisoning
food poisoning is any illness caused by eating food contaminated by bacteria or their toxins. This is common in summer months when warm temperature speed up bacterial growth and reproduction in food. food left out of fridge for a long time can contain enough bacteria and toxin to cause diarrhoea, stomach cramps, nausea, and vomiting when eaten. The symptoms are most commonly caused by campylobacter, salmonella, e coli, staphylococcus aureus, listeria and clostridium botulinum

Food poisoning from campylobacter and salmonella commonly occurs when people eat undercooked or unrefrigerated chicken containing large numbers of bacteria. S. aureus results in toxins n food such as cold meats, custards, salads and baked foods especially if the food handler had a skin infection of S. aureus.

Diseases
plant disease
The moist, temperate climate of New Zealand, where temperature and rainfall don't vary much, is ideal for growth and reproduction of disease-causing fungi and bacteria. The climate also suits insects that transport plant viruses.
Most plant diseases are caused by fungi, eg black spot, rusts, grey mould and mildew. Grey mould occurs in glass houses and infects leaves, stems, flowers and fruit of a range of different plants. Brown spots and dying plant parts are common signs. When temperatures are between 15-25 degrees or humidity is high, spores from fungus germinate, grow quickly and new fungi produce many spores. good airflow and low humidity can control outbreak of disease.
Powdery mildew disease is caused by a fungus and occurs in plants in dry conditions, such as cucumber plants. Spores contain 70% water so they dont need water to germinate. once germinated, fungus absorbs water from leaves of host plant, applying water and creating conditions of high humidity can control this disease.
Bacterial plant disease is not as common as fungal diseases but can cause much damage. eg psa attacks golden kiwi fruit plants. This disease causes brown spots, causing leaves to fall off and killing the kiwi fruit vine. 2010 outbreak was caused by unusually wet warm spring, which is ideal conditions for bacteria.

Disease in humans and other animals
Pathogenic micro-organisms cause a range of disease in humans and other animals because warm, moist bodies of humans and animals provide food and excellent conditions for the growth and reproduction. Each pathogen has its own environmental condition eg tinea occurs outside the body where skin cells become food while thrush grows inside the mouth where temperature and moisture levels are higher.

Microbial attack on material
Bacteria and spores from bacteria and fungi can grow on everyday objects made from plant and animal material like wood, cotton, leather and wool. Bacteria feed on these by extra-cellular digestion, the enzymes released breaks down the material. eg brown-rot fungus attacks wood reduces its strength.

Antibiotic resistance
In any population of living organisms, there is natural variation. This means that some bacteria in a population may carry alleles that give them resistance to an antibiotic. The bacteria carrying allele for resistance are not killed by the antibiotic so they reproduce making more bacteria resistant to that antibiotic. Over time the entire bacterial population becomes resistant to antibiotic meaning another antibiotic is needed. Extensive use of antibiotics causes more anti-biotic strains of bacteria. Unnecessary prescibing of antibotics increases exposure of a large range of micro-organisms to antibiotics, causing the development of resistant bacteria.

recycling nutrients

If not for microoganisms, the world would be covered with dead plants and animals. All dead and waste organic and inorganic material from living things is recycled when micro-organisms (saprophyte) decompose the dead and waste material - releasing the nutrients it contains into the air, soil or water. Nitrogen and Carbon are two essential nutrients recycled by micro-organisms.

Carbon cycle

Composting is the use of micro-organisms to decompose dead plant material in garden waste cycling the nutrients by making waste into nutrient rich compost used to promote plant growth. Micro-organisms make compost efficiently when they have moist, warm conditions with enough air,space and food to reproduce rapidly. Compost bins are designed to provide these.

As micro-organisms in the compost begin to decompose the organic matter and carry out aerobic respiration releasong heat energy the temperature rises. The temperature remains high during respiration and temperature decreases as decomposition is completed and micro-organisms die from lack of food or buildup of waste.

decomposition produces glucose which micro-organisms use for aerobic respiration. during respiration carbon from glucose is combined with oxygen to produce co2. This is released into the atmosphere for plants to use in photosynthesis, which continues carbon cycling.
Good airflow is important in composting so there is enough oxygen available for aerobic respiration and allow carbon cycling. If no oxygen is present and anaerobic respiration occurs, carbon remains in lactic acid.

Turning the compost increases the amount of oxygen in compost allowing aerobic respiration and heat is released which increases temperature. thermophilic microbes have a higher rate of respiration in higher temperatures. Turning compost allow microbe to break down matter more quickly. High temperature also kills pathogenic microbes and seeds in compost.

Bacteria are important in cycling carbon and nitrogen because plants need these for photosynthesis and respiration. Microbes carry out extracellular digestion breaking down dead and waste organic material . The microbes absorb nutrients and use them in respiration releasing co2 into the air which plants can use for photosynthesis. to make glucose. Glucose used in respiration to produce energy to make enzymes and chemicals needed for growth and reproduction.

Nitrogen compounds in compost are broken down by decomposers and changed into nitrates by nitrifying microbes. Plants absorb nitrates and use them to produce amino acids which becomes available to animals when they eat plants.

Useful effects of micro-organisms

• Recycling nutrients
• Food production and preservation
• sewage treatment
• producing antibiotics
• vaccine delivery
• genetic mutation in epidemiology

germination and growth in plants

Growth in plants, making new tissue, does the following- increase the height of plant - allow plant to reach light
-increases width of plant-support plant as it grows taller
produce more leaves- increases amount of photosynthesis
replaces tissue - eaten b herbivore

Germination
Seeds released from a plant can lie inactive (seeds are dormant). Seeds can stay dormant for a number of years until the right conditions
Growth of an embryo plant within a seed is germination
-germination begins with the seed taking in water. This increases the number and speed of chemical reactions occuring in the seed and embryo begins to grow. Oxygen and suitable temperature are also needed
-root of the embryo - radicle- grows first followed by plumule (shoot), As the radicle grows, lateral roots form and root hair develops. Embryo uses stored nutrients in seed to grow seedling.
Once the plumule reaches light, chlorophyll forms and plumule turns green, the seedling can carry out photosynthesis
Factors that affect germination include temperature and the amount of water and oxygen available. Light affects germination of some seeds.

Primary growth
3 processes mitosis (cell division) occurs at growing points such as apical meristem and root tips (increases cell number).
Elongation - occurs behind growing points (cells get bigger)
Differentiation - occurs further away from growing points. Cells change shape to carry out function eg xylem vessel for water transport
diagram

Secondary growth
Plants that live for longer than one or two years grow wider by secondary growth. Secondary growth occurs in the cambium layer - between the xylem and phloem in the vascular tissue
-cells in the cambium layer divide to form new cells. new cells outside the cambium layer become phloem. Older phloem become blocked and cant transport nutrient- become bark
-cells on the inside of the cambium become xylem. older xylem cant transport mineral and become wood.

Xylem formed at different times of the year are different sizes, gives wood a pattern of light and dark bands called annual rings. Xylem produced in spring is usually diameter, giving a light colour wood.

factors affecting growth
Warm temperatures increases the growth rate of plants. High temperatures can slow growth due to water loss. The greater amount of water available in spring and suitable temperatures, result in larger xylem vessels.
The amounts of nutrients in soil or growth media affect growth and photosynthesis. If some nutrients are present in small amounts or not present, photosynthesis slows, slowing growth of plant. eg magnesium needed to make chlorophyll. If soil runs out of magnesium chlorophyll moved to young leaves, older leaves can't carry photosynthesis and may die

Flower development
A plant develops modified leaves called flowers in environmental conditions are suitable. eg some plants flower only if days contain a certain number of daylight hours. A store of nutrients is also needed. in suitable conditions at least four genes known as A,B,C, and D are turned on (expressed) in cells that are to become flowers. The four genes work together to produce four parts taht each flower contains - sepal,petal,stamens and carpel

each flower begins as a disk of cells that develop into four different areas, in circles around the centre. Each area has a different combination of genes that control its development into a flower.
diagram

Plant reproduction

The purpose of reproduction is to produce offspring.

Sexual reproduction
A plant produced by sexual reproduction is genetically different to the parent plant. Sexual reproduction begins with the production of flowers from the adult plant. Pollen (male gametes) forms by meiosis in the anther of the flower. Ovules (female gametes) form in the ovary.

Pollination
Transfer of pollen from the anther to the stigma is called pollination. Pollination is successful only if the pollen is transferred between plants of the same species. Transfer of pollen from an anther in a flower of one plant to the stigma of a flower on another plant of the sames species is called cross-pollination. Self-pollination occurs when the transfer is within the same plant. Some flowers eg sweet pea are shaped to always result in self-pollination

Insect pollination occurs when an insect transfers the pollen. Plants that have insect pollination have brightly coloured flowers containing scent and nectar to attack insects. They produce small amounts of pollen with a rough surface to stick to the insect body.
Wind pollination occurs when pollen is blown from anther to stigma. Wind pollinated plants produce large amounts of light, smooth, round-shaped pollen, suitable for wind transport.
Wind pollinated flowers are often green or white because there is no need to attract pollinators. The flowers have large anthers that hang outside the flower so pollen is released easily into the wind. The stigma is feathery and hangs outside to catch pollen

Fertilisation
if pollen from a species of plant lands on a stigma of a plant from the same species, chemicals on the stigma causes the pollen to grow. The pollen grows a thin tube down the style into the ovary where the genetic material in the pollen joins with the genetic material of an ovule. This joining is fertilisation - a plant embryo forms as a result of fertilisation.

Seeds
After fertilisation, the ovules in the ovary develop into seeds. Each seed is covered by a protective testa. The seeds contains the embyro plant - radicle (first root) or plumule (first shoot), and food stored in the cotyledons. The micropyle is a small hole in the testa that allows water to enter seed to begin germination.

Fruits and dispersal
after fertilisation, the ovary of the flower develops into a fruit. Some fruits are dry and hard eg kowhai and some are soft and fleshy eg tomato. The fruit protects the seeds while they are being transported away from the parent plant - this is dispersal of the seeds. Dispersal reduces competition between parent and offspring and among offspring for resources like light and nutrients.

Different plants have different methods of seed dispersal
Explosive - hard dry fruit, forms a pod. In warm conditions the pod splits and twists spreading light round seeds eg gorse
Float - A light waterproof fruit forms carried by water eg coconut
Hooks - Fruit has a hook which catches animal fur or feather bidibids
Succulent - Fleshy fruit eaten by animal, transported away in gut
Wind - light fruit with a special shape to allow travel on the wind eg dandelion

Asexual reproduction (vegetative reproduction)
Production of new plants without making of seeds. new plants have the same genetic make-up as the parent. Asexual reproduction is quick and does not require a plant to use energy to make flowers, pollen, and fruits. Large number of offspring that grow close to the parent plant are produced. These plants can produce sexually at a different time of year.

Range of methods of asexual reproduction

Runner and stolon- shoots that grow above ground surface eg strawberry
Tuber - Swollen underground root with small buds under skin eg potato, kumara
Bulb - swollen underground leaf scale eg daffodil
Corm - swollen underground stem eg gladioli
Rhizomes - Thick underground stems that grow sideways eg iris

In some species of plants, new plants can grow from part of a plant - new dandelion plants can grow from a broken part of the main root.

Photosynthesis
photosynthesis is the process by which plants make glucose from carbon dioxide and water. To do this, green plants need chlorophyll (green pigment) and energy from light. Glucose is stored as starch when it is produced.
carbon dioxide + water ----------chlorophyll, light ----- glucose + oxygen

Leaf structures
Leaves are the main plant structure involved in photosynthesis. Leaves have the following adaptations to help them with photosynthesis.
Thin - gases don't travel far
Flat - a large surface area to trap light
Arranged on plant to trap most possible light
Green due to chlorophyll
Covered in waxy cuticle to stop leaf drying out.

The internal structure of leaves also has adaptations for carrying out photosynthesis
diagram

Testing leaves for the presence of starch
The presence of starch in a leaf is used to indicate photosynthesis has been occuring. Glucose made from photosynthesis is stored as starch in the right conditions. Iodine can be used to test for starch it turns brown to blue-black when starch is present.
Before a plant or leaf is used to test a factor for photosynthesis, it is destarched by putting it in the dark for two or three days so the plant uses up any stored starch.

To test for starch
1- boil the leaf to remove waxy cuticle
2- boil leaf in meths to remove chlorophyll as green colour would hide colour change with iodine
3- wash leaf to remove meths
4- add 3 to 4 drops of iodine
5- a blue-black result indicates starch

Factors affecting photosynthesis
-increasing the amount of carbon dioxide increases photosynthesis rate until some other factor becomes limiting eg chlorophyll amount
-increasing light intensity increases rate , up to a point
-increasing temperature increases rate, up to the optimum after which increasing temperature decreases rate of photosynthesis as enzymes are denatured
-If there is little magnesium in the soil, plant makes reduced chlorophyll
-When there is less water, the stomata closes. this limits the CO2
-changing wavelenght (colour) of light changes rate. chlorophyll does not absorb green light (reflected). Blue and red light produces highest rate of photosynthesis, yellow produces lower and green the lowest.

To show light is necessary for photosynthesis
diagram
to show co2 needed for photosynthesis
diagram
to show chlorophyll needed for photosynthesis
diagram
oxygen needed for photosynthesis
diagram

Bacterial and Viral infections

• In a person infected with a virus, the symptoms develop much more quickly. This is because when viruses reproduce they infect a living cell and use the materials and structures already inside that cell to produce many more viruses. One virus can produce many viruses at the same time which can infect more cells immediately so symptoms occur quickly.

• In a person infected with a bacteria, the symptoms develop more slowly because it takes time for the numbers of bacteria to increase to a level where effects are felt. for example a small number of bacteria producing toxins wont have a big effect but as the numbers of bacteria increase, more toxin is produced so the symptoms slowly develop. Bacteria divide by binary fission and can divide every 20 minutes in suitable conditions but the numbers build up slowly compared to viruses. Bacteria also have to feed and build up materials and energy to reproduce which viruses do not have to do.

Revision--Micro-organism reproduction

• Bacteria reproduce by binary fission. First, the genetic material is copied and then the cell divides in two so each cell gets a copy of the genetic material and some cytoplasm.

• Virus require a living host to reproduce. Some types attach to the outside of the host cell and the genetic material is released inside the cell. The genetic material causes the host cell to make copies of the virus genetic material and produce a protein coat so new viruses are released from host cell.

• Fungi produce spores to reproduce. Sporangia develop and when ripe burst open releasing spores. Spores germinate and grow a new fungus.

A similarity between bacteria, virus, and fungi reproduction is that all three copy the genetic material so new individuals always receive an exact copy of the genetic material (asexual reproduction-genetically identical offspring).
A similarity between viruses and fungi is that many offspring are produced each time whereas bacteria only produce two cells each time.

The main difference with viruses is the need for a host cell that puts together the virus parts. Sometimes the host cell dies as it bursts open to release virus. However, bacteria and fungi reproduce on the food source they are growing on, which need not be living.

A difference between bacteria and fungi that bacteria do not have specific structures related to binary fission. The bacterial cell can divide into two cells whereas fungi must develop reproductive sporangia that ripen and burst to release many spores that germinate and grow into new fungi.

The science of making bread

• When supplied with water and sugar, but no oxygen, yeast reproduce and carry out anaerobic respiration (fermentation) to produce carbon dioxide, ethanol and a little energy.
• Yeast obtains the nutrients by extra-cellular digestion. Enzymes released from yeast into the food source digest the sugar releasing glucose. The smaller glucose is absorbed into the yeast.
• An experiment was done to determine the best (optimum) temperature for anaerobic respiration using yeast mixed with sugar and water in a bottle. Foam is produced due to the carbon dioxide and the level was highest a 40 degrees showing the most carbon dioxide produced. That is the optimum temperature.
• When bread is being made the yeast, sugar, water mixture is warmed so the rate of anaerobic respiration increases quickly reducing the time taken to make bread. 
• When yeast is stored, it should be at 20 degrees so yeast respire slowly. The container yeast is stored should be sealed to keep out moisture. With no water the glucose and enzymes can't move and collide so no fermentation occurs.
• If respiration is high when stored, the yeast can die from a lack of food. The low temperature of  a fridge can also slow respiration so no energy is available for reproduction which increases the time yeast remains alive in storage.

Bacterial growth

Bacteria reproduce by binary fission. Once a bacterium reaches maximum size, the genetic material is copied and the cell splits in two. Each new bacteria grows then splits in two. If there plenty of food, moisture and warmth, bacteria can reproduce every 20 minutes.

The above graph shows a typical bacterial growth curve. At the start of the graph there is only a small number of bacteria. They reproduce by binary fission so numbers increase slowly (2 to 4 to 8 to 16). However each time the number doubles, so the bacterial population increases very quickly (5000 to 10000 etc). A fast rate of reproduction continues until a factor (lack of food, space, water, build up of toxins, cooler temperature) limits bacteria reproduction, shown by the curve leveling off. The end curve shows a reduction because of the death of bacteria due to the limiting condition.

One way to reduce food poisoning is to maintain food in conditions that limit bacterial reproduction. eg cool temperatures in the fridge don't kill bacteria but reduce reproduction.

Effects of environment II

Nutrients and Moisture

 Different micro-organisms have different nutrient requirements but all require an energy source, moisture(water), vitamins and minerals. The presence of suitable nutrients determine if micro-organisms can grow in the food source or not. eg milk is rich in nutrients so is a good environment.

Water is essential for all living things as a substance in which chemical reactions take place and materials are transported. If there is no water, micro-organisms can't grow and reproduce.

Chemicals

• pH -- Different micro-organisms have different optimum (best) pH and a range of pH they can live in. Outiside the optimum pH, rate of growth slows as enzymes are sensitive to the pH. Most bacteria prefer pH between 6-8, but lactic acid bacteria can grow in a much lower pH (Acidic places) so they can outcompete other bacteria in those places.
• Toxins -- Poisonous wastes produced by micro-organisms which can kill them in high concentrations.
• Antibiotics -- chemical  that kill bacteria or slow there growth. eg penecillin made by a certain bacteria.
• Disinfectants -- chemicals that kill or break down micro-organisms. eg bleach, peroxide. These join onto the cell wall and enter the cell, disrupting the cell membrane or DNA and stop life processes such as the transport of material.
• Antiseptics -- disinfectants used in skin eg hydrogen peroxide. This joins to enzymes and destroy their structure (denaturing).  

Competition

Micro-organisms can make chemicals that help them out-compete others. eg fungi produce antibiotics that kill bacteria, reducing competition for space and nutrients. Lactic acid bacteria also produce chemicals that kill other bateria.

Host species

Viruses and pathogenic bacteria/fungi require a host cell to grow. Few host cells mean growth and reproduction of pathogen is reduced.

Effects of environmental factors

Environmental factors such as temperature, availability of oxygen, water and nutrients and the presence or absence of various chemicals affect the rate of growth and reproduction of micro-organisms.

Temperature 

Different micro-organisms have different optimum (best) temperatures at which they grow and reproduce most quickly. Eg parasites of human grow best at 37 degrees as that matched the human body temperature.

 Saprotrophs grow best in temperatures around 30 degress but can grow between 5 and 45 degreess. This is an advantage as they grow on material that is always changing temperature ( eg night and day). Growth and reproduction are slower in temperatures above or below the optimum because of the effect of temperature on processes such as enzyme activity and diffusion. 

Oxygen availability

Aerobic micro-organisms require oxygen in their environment. Some require lots of oxygen, others very little. Eg helicobacter and campylobacter require very little oxygen so they can survive in the human gut. Aerobic respiration uses glucose and oxygen. Carbon dioxide water and a lot of energy is released. Increasing the amount of oxygen increases growth rate of the bacteria up to a certain point when another factor becomes limiting.

Anaerobic micro-organisms do not require oxygen. Lactic acid bacteria (used to make yoghurt) are anaerobic. They produce usable energy by the process of fermentation( a type of anaerobic respiration).

Yeast can respire both aerobically and anaerobically. Aerobic respiration produces more energy but if the oxygen is used up, yeast can produce energy anaerobically by fermentation. During fermentation, ethanol (alcohol) is produced but if fermentation s carried out too long the high amount of ethanol kills the yeast.

Culturing Micro-organisms

The conditions micro-organisms need to grow and reproduce on agar plates are food, moisture and warmth. If plates are left open, micro-organisms (eg spores from fungi) can land and grow. We can also use cotton swabs to grow bacteria on the plate. The nutrient agar provides water and food. Placing the plates in an incubator at 25 degrees provides warmth.

Bacteria reproduce quickly by binary fission, producing millions of colonies that are visible as shiny dots due to the slimy capsule around bacteria.

Fungi look furry because of the hyphae. The darker areas are where the fungi are producing sporangia with asexually produced spores. These grow above the surface so the spores can be carried by wind.

Both bacteria and fungi are saprotrophs, so they can digest nutrients on the plate and reproduce.

Viruses can't grow on agar plates as viruses must have a living cell as a host to enable them to carry out reproduction.

Bacteria and Fungi feed by Extracellular digestion

• Both bacteria and fungi feed by extra-cellullar digestion. 
• Digestion occurs outside the cell. Enzymes are released by the hyphae or bacteria ont food particles outside the cell. The enzymes breakdown (digest) the food and the nutrients are absorbed