B4 - It's a green world

Habitat = where a plant or animal lives

Population = number of a particular plant or animal present on the community 

Biodiversity = a large variety of plants and animals that live in an ecosystem

Distribution of organisms is mapped using a transect line:

• a long length of string is laid accross an area
• at regular intervals the organisms in a quadrat are counted (for animals) / assessed for % cover (for plants)
• data is displayed on a kite diagram

Artificial ecosystems = humans deliberately keep and protect only one species and remove other organisms that would compete with it -> for the benefit of humans 

Food chains / webs show plants and animals are intedependant. Exchange of gases in photosysnthesis and respiration ensures overall balance of these gases therefore an ecosystem is self-supporting in all factors apart from having to depend on the sun as an energy source.

Population sizes can be estimated:

• using capture - recapture method:
  • Population size = 
  • (number in 1st sample x number in 2nd sample) / number in 2nd sample previously marked

Assumptions made:

• there are no deaths or reproductions and no movement of animals in and out of area
• identical sampling methods are used for all samples
• markings of animals do not affect survival of animal

Balanced symbol equation of photosynthesis:

• 
• simple sugars like glucose can be:
  • used in respiration to release energy
  • converted into cellulose to make cell walls
  • converted into proteins for growth and repair
  • converted into starch, fats and oils for storage:
    • starch is insoluble and cannot move from storage areas which is why it is used for storage
    • it also does not affect water concentration of cells and cause osmosis
• Photosynthesis contains two stages:
  • water is split up by light energy releasing oxygen gas and hydrogen ions
  • carbon dioxide gas combined with hydrogen ions producing glucose and water
• Modern experiments using Chlorella and oxygen-18 have shown that light energy is used to split up water molecules, not carbon dioxide

Rate of photosynthesis can be increased by having:

• more carbon dioxide which produces more oxygen
• more light which provides more energy to split up water molecules
• a higher temperature which increases enzyme action making the rate faster

Respiration happens ALL OF THE TIME:

• The rate of gas exchange in photosynthesis is greater than that of respiration in terms of quantities so respiration can only be noticed at night in darkness.

Photosynthesis depends on light, temperature and carbon dioxide which is why a lack of these factors will limit the rate of photosynthesis. These factors are limiting factors.

Adaptations for efficient photosynthesis:

• outer epidermis lacks chloroplasts, is transparent so there are no barriers to entry of light
• upper palisade layer contains most chloroplasts, recieve the most light
• spongy mesophyll cells loosely spaced so that diffusion of gases between cells and outside can take place
• arrangement of spngy mesohpyll cells create large surface area to volume ratio

Leaf adaptations for photosynthesis:

• broad in shape to have a large surface area so as much light as possible is used
• thin so gases can diffuse easily and light gets to all cells
• contain chlorophyll and other pigments to maximise use of suns energy as each pigment absorbs light of different wavelengths
• have a network of vascular bundles for support and transport of chemicals like water and glucose
• specialised guard cells which control the opening of stomata to regulate flow of carbon dioxide and oxygen

Diffusion = net movement of particles in a gas / liquid from an area of high concentration to an area of low concentration

Leaf adaptations to increase rate of diffusion:

• a large surface area
• stomata
• gaps between spongy mesophyll

Rate of diffusion can be increased by having:

• a shorter distance for molecules to travel
• a steeper concentration gradient 
• a greater surface area for molecules to diffuse from / into

Osmosis = the movement of water molecules across a partially permeable membrane from an area of high concentration to an area of low concentration 

What happens to plant cells when water enters / exits cells:

When water enters plant cells:

• plant cell becomes turgid, there is more pressure pushing against cell wall

When plant cells lose too much water:

• cell contents shrink, become plasmolysed (cell membrane shrinks away from cell wall), and cell is called flaccid

When too much water enters animal cells:

• they lack a cell wall so water enters and causes cell to swell up and burst (lysis) 

When too much water is lost from animal cells:

• cell shrinks = crenation

Xylem:

• carry water and minerals from roots to leaves, involved in transpiration
• called vessels, made of dead cells, lack of living cytoplasm
• cellulose walls have an extra thickening of lignin to make it strong and waterproof
• one way transport

Phloem:

• carry foods substances e.g. sugars to growing and storage tissues, involved in translocation
• living cells, arranged in columns
• two-way transport

Transpiration:

• evapouration and diffusion of water from inside the leaves
• loss of water from inside leaf helps create continuous flow of water from the roots to leaves in xylem cells

Leaf adaptations to prevent too much water loss:

• having a waxy cuticle that covers outer epidermal cells
• guard cells are able to change the size of stomata :
  • photosynthesis in guard cells produces sugars, increasing turgor pressure, causing guard cells to curve

Efficient photosynthesis:

• stomata allow entry and exit of gases
• spongy mesophyll cells are covered with a film of water so gases can dissolve easily

Rate of transpiration can be increased by:

• increase in light intensity, stomata open up
• increase in temperature causes an increase in evapouration
• increase in air movement, blowing away air containing evapourated water
• decrese in humidity, allowing more water to evapourate

Soil Minerals plants need: 

• nitrates: for protein synthesis which is used for cell growth
  • lack of nitrates causes poor growth and yellow leaves
• phosphates: involved in respiration and growth
  • lack of phosphates causes poor root growth and discoloured leaves
• potassum compounds: involved in respiration and photosynthesis
  • lack of potassium causes poor flower and root growth and discoloured leaves
• magnesium compounds: involved in photosynthesis
  • lack of magnesium causes yellow leaves

Soil minerals are used by the plant to produce:

• nitrogen: to produce amino acids to form a variety of proteins
• phosphorus: to make DNA and cell membranes
• potassium: help enzyme action in photosynthesis and respiration
• magnesium: to make chlorophyll

How minerals are taken up by plants:

- Minerals are present in soil in low concentrations

- Minerals are taken up by root hair cells by active transport

- Carriers across the cell membrane transport selected minerals into the cell where there is already a high concentration of minerals

- Active transport enables minerals to be transported against the usual method from high concentration to low concentration (concentration gradient)

- Transporting against the concentration gradient requires energy from respiration 

Detritivores: e.g. earthworms, maggots and woodlice, feed on dead and decaying material (detritus)

• increase rate of decay by breaking up detritus to increase surface area for further microbial breakdown

Saprophytes: e.g. fungi, feed on dead and decaying material

• produce enzymes that digest food outside their cells and reabsorb simple soluble substances = extracellular digestion

Factors increasing rate of decay:

• temperature: increasing temperature increases bacteria / fungi 's rate of respiration
• oxygen: increasing amount of oxygen means bacteria will use aerobic respiration to grow and reproduce faster
• water: increasing amount of water allows materials to be digested and absorbed more efficiently and increases growth and reproduction of bacteria and fungi

Food preservation: -->reduces rate of decay

• Canning:
  • foods are heated to kill bacteria and sealed in a vacuum to prevent entry of oxygen and bacteria
• Cooling foods: (keeping food in the fridge)
  • slow down bacterial and fungal growth and reproduction
• Freezing foods: (keeping food in the freezer)
  • kill some bacteria and fungi and slow down growth and reproduction
• Drying:
  • removes water so bacteria cannot feed and grow
• Adding salt / sugar:
  • kills some bacteria and fungi because of high osmotic concentration removing water from them
• Adding vinegar:
  • produces very acidic conditions killing most bacteria and fungi

Pesticides: (e.g. insecticides, fungicides, herbicides)

• enter and accumulate food chains, becoming a danger for predators
• can harm other organisms that are not pests
• some are persistent - take a long time to break down 

Organic farming: doesn't make use of artificial fertilisers or pesticides

• uses animal manure and compost, crop rotation, nitrogen-fixing crops and varying seed planting
• crops are smaller and produce is more expensive

Biological control: uses living organisms to control pests

• avoids disadvantages of artificial insecticides, do not need replacing
• introduced species eats other useful species, population increases and become pests themselves
• can interfere with other organisms of food web causing unexpected results

Intensive farming: makes use of artificial fertilisers and pesticides to produce large crop yield cheaply and efficiently

Hydroponics:

• system uses a regulated recycling flow of aerated water containing minerals
• useful in areas of barren soil or low rainfall
• better control over mineral levels and disease, many plants can be grown in a small space
• concerns about extensive use of chemicals on plants

Intensive farming:

• improves efficiency of energy transfer in food chains by reducing/removing competing organisms 
• Battery farming:
  • by keeping aimals in barns or sheds, they use less energy to keep warm and to move
  • more energy can be used on growth or egg production