B4 revision

Sampling techniques

Why sample?

• Might need to locate and study the distribution of an organism of one species.

• They might need to know the number of species within a given area.

• By studying the distribution of organisms they can look at the possible relationships between organisms by seeing where their distributions overlap.

Distribution- scientists record the location of one species

Population –scientists record the number of organisms of a particular species in an area.

Community – scientists record the different populations of species in a particular area.

Relationship –scientists study how the distributions of different species overlap to see if there is a relationship between the species.

Sampling – counting a small number of a total population of a particular species, and then estimating the total from the sample.

Sampling techniques

Quadrat- quadrats are frames of a certain area which can be thrown randomly on the ground and the number of organisms of a particular species counted. Useful for estimating plant numbers.

Transect lines –

Transect lines are tapes that are laid down across an area of interest. You can either count organisms that touch the tape, or lay quadrats at regular intervals to count the organisms and determine their distribution. Useful technique for estimating numbers of plants.

Nets –

Used to catch animals such as butterflies and fish to count and record animals.

Pooters –

Small organisms such as insects on bushes or trees can be sucked up into a collecting chamber to be identified and counted.

Pitfall Traps –

These are small containers that are buried in the ground, and small animals such as walking insects will fall in and can be counted and identified.

Capture-recapture –

This is a technique where you capture organisms in an area (first sample), count them, mark them, and then release them.

At a later date, you take a second sample of organisms in that area, and record the total in the second sample, and then count how many of these have a mark on to show that they were captured in the first sample.

You then estimate the population size using the following equation:-

Number in first sample x number in second sample

Number in the second sample previous marked

e.g. total number collected and marked in sample 1 = 36

total number collected in sample 2 = 23

Number marked in the sample 2 = 14

Total population = 36 x 23

14

= 59.1

= 59

You cannot have .1 of an organism so you round it up or down

Improving sample accuracy

• Sample size- Apparatus should allow of lot of one type of organism to be counted (small sample sizes are less accurate).

• Reliability- repeated sampling increases reliability

• Fair test- same equipment, random placing of quadrats to reduce bias.

Identifying organisms

Keys – are used to identify plants and animals

Spider key – answers to questions take the reader along one of two branches

Numbered key –

Statement Answer

1. Does the animal have four legs? Yes - go the statement 2

No - go to statement 4

2. Does the animal have a curly tail? Yes - pig

No - go to statement 3

3. Does the animal have a hoof divided into two parts? Yes - cow

No - horse

4. Does the animal have webbed feet? Yes - duck

No - human

Questions are in a list, and you are sent to another numbered question

Natural ecosystems

Ecosystem – includes all the living things in an area i.e. the community, how they interact with each other, and the physical conditions around them.

Ecosystems only require energy for the sun as they are self-sufficient.

Examples of natural ecosystems include woodlands, lakes, and seashores. They often contain many different types of organism so are said to have a high biodiversity.

The distribution of organisms is not random but is influenced by physical factors (availability of water), and effect of other organisms (lots of predators).

Zonation and data displayed in kite diagrams

If scientists wanted to look at the distribution of two species, they could set up a transect line on the area of interest, and using quadrats they could take regular counts of the two species along the transect line. The data is then displayed in a kite diagram like the one above. The kite diagram above shows that as distance increases there are fewer dandelions and the grasses take over.

If species live in different bands or zones in an area- this is called zonation. There could be physical reasons why one species does better than another in a zone.

Artificial ecosystems – these are created by humans e.g. fish farms, gardens.

Usually are fewer types of organisms (lower biodiversity) as humans remove all unwanted species.

Photosynthesis

Plants contain a green pigment called chlorophyll (in chloroplasts) which traps light energy from the sun. This energy is used to build carbon dioxide and water into carbohydrates and oxygen. Process is called photosynthesis.

Balanced symbol equation

C6H1206 + 6O2 6C02 + 6H20 + energy

This is really hard to remember, but if you learn the word equation, and the chemical formula for glucose, the balancing is easy - 666.

Photosynthesis occurs in 2 stages

1. Light energy splits water into waste oxygen gas and hydrogen ions.2. Hydrogen ions combine with carbon dioxide to form glucose and some water that is

used up during photosynthesis (can occur day or night).

What does a plant make during photosynthesis?

• Glucose- is used for respiration in the plant cells, and any not being used can be stored in the plant.

• Oxygen- is used in the plant for respiration to produce energy, and is released via stomata into the air for animals to breathe.

What other substances is glucose converted into?

Glucose is used for respiration at night.

Glucose is converted into sucrose for transport around the plant as it dissolves in water and flows easily.

Why glucose is stored as starch

• Starch is insoluble, will not dissolve in water and flow out of the plant cells.

• Starch does not affect the water concentration inside cells

• Starch can be converted back into glucose when needed for respiration.

Photosynthesis and respiration

Daytime

Night-time

Photosynthesis is at a greater rate than respiration, so there is a net movement of oxygen out of the plant.

No photosynthesis occurs, just respiration

Rates of photosynthesis

Factors that affect the rate of photosynthesis

• More carbon dioxide

• More light

• Warm temperature

These factors are called limiting factors as they can limit the rate of photosynthesis.

Plants grown commercially in glass houses have a faster rate of photosynthesis as there are lighting systems, and heaters that burn fuels which release carbon dioxide gas.

Effect of light intensity

The more carbon dioxide that is available the faster the rate of reaction, but rate will stop increasing due to the limiting factors of light or temperature.

Effect of temperature

• If light levels were low, you could increase the temperature and the rate of photosynthesis could increase up to a point (photosynthesis is an enzyme controlled reaction).

• However, if the plant becomes too hot the enzyme denatures and the plant dies.

Leaves and photosynthesis

Leaves are the main plants organs for making food.

Inside of leaf structure

Adaptations of a leaf for photosynthesis

• Large surface area to absorb light

• Thin so gasses don’t have far to diffuse

• Containing chlorophyll

• Network of veins to transport water and sugars

• Having stomata to allow gasses to diffuse in and out

• Upper palisade layer that receives most of the light, contains most of the chloroplasts

• Air spaces in the spongy mesophyll to provide a large surface area/volume ratio for absorption of gases.

• Epidermis is transparent to allow light through to the palisade cells.

Scientists and the history of ideas about photosynthesis

• Ancient Greeks thought plants grew as they absorbed minerals from the soil.

• Van Helmont just watered a plant he kept in the same pot, the plants mass increased, but the soils mass hardly changed. He concluded that absorbing water made it grow.

• 1771- Joseph Priestly grew mint leaves in a sealed chamber containing mice and the mice survived as the plant provided them with oxygen.

• Recently, using isotopes, scientists have determined that oxygen given out by plants during photosynthesis comes from the water and not the carbon dioxide.

Diffusion

• Is the random movement of particles from a high concentration to a low concentration down a concentration gradient until they are evenly spread out.

• If there is a steep difference in the number of particles, diffusion is faster (like skiing

down a steep hill, you would go faster).

Diffusion in cells – dissolved substances enter and leave cells by diffusion e.g. oxygen, carbon dioxide. They enter and leave the cell through small holes in the cell membrane. No energy is required for diffusion as molecules move from a high to a low concentration spontaneously.

Factors affecting rate of diffusion

Distance – the shorter the distance the particles have to move, the faster the diffusion. Leaves are thin so that there is a short distance for the diffusion of gases in and out of the leaves.

Concentration gradient – the greater the difference in concentration of molecules between 2 regions, the faster the rate of diffusion.

When oxygen is made by photosynthesis, there is a build up inside the leaf (a high concentration), and so diffusion of oxygen to the outside is fast.

Surface area – larger the surface area that the particles have to diffuse across the faster the rate of diffusion e.g. internal surface of a leaf is large.

Osmosis

• Is a special type of diffusion which involves water moving through pores (holes) in a semi-permeable membrane (allows water through but not larger things such as sugar).

• The overall net movement of water from an area of high concentration of water to an area of low concentration of water across a semi-permeable membrane.

Plant cells take up water by osmosis and become firm. When the contents of the cells are pushed up against the cell wall, the cell becomes turgid and this helps support the plants. If cells lose water, there is less pressure against the cell wall and the cells are flaccid (floppy). If it loses too much water, the plasma membrane and cell contents come away from the cell wall and the cell is said to be plasmolysed.

If animal cells are placed in a dilute solution, water moves into them and they burst as they do not have a cell wall, this is called lysis. If an animal cells in placed in a more concentrated solution, the cells lose water and becomes crenated.

Plant structure

Plants have a number of different organs.

[tissue – group of similar cells working together, organ – made up of different tissues working together]

Vascular bundles – contains the tissues xylem and phloem which transport substances around the plant and support it.

Xylem – cells in the xylem are dead and have a hollow cavity called a lumen. Stacked on top of each other they form hollow vessels through which water and minerals are transported from root to leaves.

Phloem – phloem cells are living, are stacked on top of each other to form tubes through which food substances are transported from leaves to the rest of the plant.

Support in plants

Vascular bundle in leaf

Vascular bundle in a stem

Vascular bundle in a root

Xylem vessels have thickened cellulose cells walls to add support.

Vascular bundle in root – in the centre of root and helps it to act like an anchor. Root allows plant to bend in the wind.

Vascular bundle in stem – located around edge to provide strength in a breeze

Vascular bundle in leaf – supports softer leaf tissue

Transport in plants

Transpiration stream – this is the movement of water and minerals in the xylem

Translocation – movement of sugars in the phloem from the leaves (source) to areas of the plants where it is needed (sink).

Transpiration

Roots have root hairs which produce a large surface area to absorb water from the soil

Water flows up the steam and exits the leaves by evaporation and diffusion (loss of water from the leaves is called transpiration).

Water is needed in plants for – photosynthesis, cooling effect as it evaporates from the leaves, supports the plants by making cells turgid, transports mineral through the plant.

Process of transpiration –

Controlling water loss

Waxy cuticle- waterproof layer on upper and lower surface of leave to prevent water evaporating through it

Stomata – can be opened and closed (open during the day for photosynthesis, closed during the night when photosynthesis does not occur). When stomata are closed, water is not lost.

Guard cells and control of opening and closing of stomata

Factors affecting the rate of transpiration

• Increased light intensity

• Increase temperature

• Increased air movement

• Decrease in humidity

Light intensity

When conditions are good for photosynthesis, the guard cells are turgid, opening the stoma. Oxygen can enter the leaf and water can leave.

When conditions are not good for photosynthesis, the guard cells close the stoma. This reduces water loss.

When light intensity increases the stomata open (to allow gas exchange for photosynthesis). This increases the rate of water evaporation from the leaves so transpiration is increased

Increase in temperature

Increased air movement

Decreased humidity

Plant minerals

Plants need minerals to remain healthy and without them they show deficiency symptoms.

Minerals come from the soil and are taken up against the concentration gradient (more minerals in the roots than in the soil), and this requires energy (think of pushing your bike up a hill and this require energy). The energy is provided by active transport and a protein carrier is required.

As temperature increases, water molecules move faster and evaporate from the leaf, so transpiration rate is increased

When air moves over a leaf, it moves evaporated water molecules away from the leaf.

The faster the air movement, the faster water will be removed, keeping a high concentration between in the inside of the leaf and the outside.

When there is less water in the air (less humid), there is a greater concentration gradient of water between the inside and the outside of the leaf.

Minerals can be added to soil by adding animal manure (decays and releases minerals slowly), compost or rotting leaves (decays and releases minerals slowly), or adding chemical fertilisers which dissolve and release minerals into the soil quickly.

Which minerals do plants need?

Potassium is a mineral which is required by plants. It attaches to the protein carrier, and the protein carrier uses energy to change shape and potassium goes through the root hair cell membrane, and into the root cell.

NPK ratio

Fertilisers list the amount of nitrogen (N), phosphorus (P), and potassium (K), as the NPK ratio. Different fertilisers will differ in their NPK ratio. High nitrogen fertilisers promote growth and high potassium flowering.

Decay and recycling

Natural recycling – nature breaks down dead plants and animals and returns elements such as carbon and nitrogen for reuse.

Microbes as recyclers – two types, bacteria and fungi are involved in decay.

Microbes in compost heaps break down grass cutting etc, and the compost produced can be used for growing plants.

Microbes in sewage works break down sewage from homes. Bacteria are in large tanks and digest the sewage matter.

Factors affecting the rate of decay

Breaking down of dead matter

2 main groups

Detritivores – e.g. earthworms, maggots, east small parts of dead material, they digest it and release the waste. This increases the surface area of the dead matter for decomposers to break down.

Decomposers – bacteria and fungi chemical break down dead matter, releasing ammonium compounds to the soil (contain nitrogen for growth). Most decomposers are saphrophytes, these release enzymes on to dead material which digest it (extracellular digestion), then absorbed the nutrients.

Preventing decay

Food decay results in less food for people to eat, and profits for farmers and supermarkets is reduced.

Methods of preventing decay

Canning – food in cans sealed can are heated to a high temperature to kills microbes. Sealing of the can prevent oxygen entry.

Cooling- fridge slows bacterial reproduction

Freezing- stops microbes that can cause food decay reproducing

Drying- without water, decomposers cannot grow or reproduce.

Adding salt – salt causes water to be drawn out of food, so microbes cannot grow and reproduce.

Adding sugar- same effect as salt

Adding vinegar- vinegar is an acid which kills microbes.

Intensive farming

Intensive farming attempts to maximum amount of food per hectare of land.

Examples of intensive farming is battery hens, and the use of artificial fertilisers and pesticides.

Advantages – high yield of food per unit of land, low food production as maximum production is achieved by using fertilisers, and less labour intensive as chemical and machines means people do not have to spread fertiliser on the land or pull out weeds.

Disadvantages – pesticides can build up in the food chain, fertiliser of soluble can get washed into streams and lead to pollution, and rearing animals in small enclosures is unethical and disease spread quickly. Organophosphates fill insects in sheep wall but caused nervous system problems in farmers.

Pesticides – include insecticides that kill insects (which eat the crops), fungicides (decay crops, make farm animals ill), herbicides kill weeds which compete with crops. Pesticides reduce damage to crops and herd and so there is an increase in yield and so more profit for the farmer.

Futuristic farming

To get ever-larger increases in yield, new techniques have been developed e.g. fish farming, glasshouses and hydroponics.

Fish farming – fish are bred in large cages in rivers and seas. Increased yield of fish as less predation, easier to catch, fish are cheaper, and gives a chance for wild fish numbers to recover. Disadvantages are that as fish are close together, disease can spread quickly.

Glasshouses – Used to grow crops out of season. Can control temperature inside the greenhouse with heaters and ventilation. Pesticides and fertilisers are contained inside the greenhouse, diseases easily treated.

Hydroponics – this is where plants are grown without soil.

Organic farming

No artificial chemicals are used to grow crops. Compost and manures are used as fertiliser to promote plant growth. These improve the texture of the soil and minerals are released slowly as the manure and compost break down. Sometimes it is difficult to get enough manure.

Weeds are pulled out by hand and this is labour intensive.

Crop rotation - planting fields with different crops in a cycle. By planting fields with leguminous plants (have nitrogen-fixing bacteria in root nodules), nitrates are added to the soil.

In organic farming, farmers vary their seed planting times, and plant in batches. This means that crops are harvested in small numbers.

Biological control of pests - predators to the crop pests are introduced to kill them. Advantages are that no artificial chemicals are used, and where artificial chemicals may not last long, predators stay around longer. Disadvantages- predator may not eat pest, predators may eat useful species, the predators may increase in number and become a pest, the predator may not stay in the area where they are needed, and the food web may be affected.