Standard Grade Biology – Revision Notes
The Biosphere
Habitat – where an animal lives
Community – all the plants and animals in an area
Ecosystem – living and non living parts (habitat + community)
Population – living organisms of one type
Biotic factor – a living factor (disease, predators)
Abiotic factor – a non – living factor (temperature, pH)
Sampling - taking a small section of the area to get an idea of as a whole.
Quadrat - estimate numbers of plants. Throw randomly, take many samples (reliable), make a
general rule for counting and stick to it.
Tree Beating – sample a tree. Do many samples,
The Nitrogen Cycle
• The cycling of Nitrogen (needed by humans to make protein).
• lightening and fixing of nitrogen gas (from air) into nitrates in the soil = nitrification
(nitrogen into the soil).
b+f
b
b
• plant protein ⇒ animal protein ⇒ death and decay ⇒ ammonium ⇒ nitrites ⇒ nitrates
n
n
b = bacteria
f = fungi
n = nitrification
• nitrates ⇒ nitrogen gas in the air (by bacteria) = dentrification (removing nitrogen from the
soil).
Investigating Cells
• Animal Cells – nucleus (controls cell activities); cell membrane (controls what substances can
enter and leave the cell), cytoplasm ( jelly like material where chemical reactions take
place).
• Plant Cells – nucleus, cell membrane, cytoplasm, cell wall ( made of cellulose and gives cell its
shape), vacuole ( contains cell sap), chloroplasts (site of photosynthesis, contains
chlorophyll).
nucleus (controls cell activities); cell membrane (controls what substances can enter and leave
the cell), cytoplasm ( jelly like material where chemical reactions take place).
• Diffusion – the movement of molecules from a region of high concentration ⇒ a region of low
concentration, until equal. Only small soluble molecules (glucose) can diffuse in and out of a cell
as they have to pass through tiny pores in the cell membrane (selectively permeable).
• Osmosis – the movement of water molecules from a region of high water concentration ⇒ a
region of low water concentration through a membrane and down a concentration gradient.
• Animal cell + water ⇒ burst (no cell wall); animal cell + 0.85% salt ⇒ same;
animal cell + strong salt / sugar ⇒ shrink
• Plant cell + water ⇒ turgid (doesn’t burst); plant cell + dilute salt / sugar ⇒ same;
plant cell + strong salt / sugar ⇒ plasmolysed
Mitosis – a summary
• The process by which the nucleus divides into two daughter nuclei, each becoming an identical
copy of the mother nucleus.
1) Chromosomes appear as long strands
2) Chromosomes become shorter and thicker, made of two chromatids, joined by a
centromere
3) Chromosomes line up along the equator and are attached to opposite poles by a spindle
fibre.
4) Chromatids are separated as the centromere splits and they are pulled to each pole
(north and south).
5) The separate chromatids are now called chromosomes and the cytoplasm starts to divide
and a nuclear membrane forms around the chromosomes.
6) Two daughter cells are formed which are identical copies of the original cell.
Enzyme – Summary
• Biological catalysts )made of protein) that speed up the rate of reactions. They can be
breakdown (degradation) or Build up (synthesis) reactions.
• Substrate
⇒
Enzyme
⇒
End Product
(what you start with)
(biological catalysts)
(what you end up with)
• Enzyme rate is affected by temperature and pH. All enzymes work best at 370C.
• Pepsin works best at pH 2.5 and catalase works best at pH 9.
• Enzymes are therefore said to be “specific” and work best at their “optimum”.
• Enzymes work like a “lock and key”. The substrate is the key and the enzyme is the lock/
• The enzyme remains unchanged at the end of the experiment and can be reused.
Substrate
Starch
Hydrogen Peroxide
Protein
Fat
Glucose – 1 - phosphate
Enzyme
Amylase
Catalase
Pepsin
Lipase
Phosphorylase
End Product
Maltose
Water and oxygen
Peptides
Fatty acids
Starch
Synthesis / Degradation
D
D
D
D
S
• Living things need energy to grow, move, reproduce etc. They get this energy from Aerobic
Respiration.
• Aerobic Respiration –
glucose + oxygen ⇒ carbon dioxide + water + energy
• Metabolism – the sum of all chemical processes in a living organism that keeps it alive.
World of Plants – A Summary
• Plants are used for food (wheat), medicine (opium from poppies) and as raw materials (timber).
• The rainforest should not be destroyed as it may house new foods and new medicines. These
are potential uses of plants.
• Germination – the development of a plant embryo into a plant. It requires water(allows
enzymes to digest the stored food), oxygen (for respiration) and a suitable temperature (for
enzymes).
• Photosynthesis – food production (starch) by a green plant. It needs light, carbon dioxide and
chlorophyll.
Enzyme controlled
carbon dioxide + water + light energy
⇒
sugar (stored as starch) + oxygen
• A seed contains
1) Seed coat – protects the internal structures
2) Food store – gives the young plant energy for growth
3) Embryo plant – grows into the plant
• Pollination – the transfer of pollen grains from the anther to a stigma. It can be selfpollination or cross-pollination. Cross-pollination can be done via the wind or an insect (e.g. bee).
Insect Pollination
Flowers - responsible for the reproduction of the plant (ovules are female gametes and pollen
are male gametes).
1) Petal – bright in colour to attract insects
2) Stamen – male part, contains pollen. Divides into the anther (splits to release pollen) and
the filament.
3) Ovary – female part, contains ovules
4) Nectary – makes sugary nectar that insects eat
5) Sepal – protects the unopened flower.
6) Stigma – pollen grains attach here, it is sugary and sticky.
• Once a pollen grain has landed on a stigma, it responds to sugar on the stigma and uses it as
energy to produce a pollen tube, which grows down the stigma. The nucleus of the pollen grain
travels down to reach the ovule where the male and female gametes fuse forming a zygote
(fertilisation).
Wind Pollination
• The flowers are small and do not have bright colours or a nectary (they do not need to attract
insects).
• The anther is attached loosely and hangs out of the flower (allows them to be shaken).
• The pollen grains are light and smooth and a large quantity is produced (allows them to be
carried by the air and there is a smaller chance of the pollen reaching the stigma).
• The stigmas are feathery and hang outside of the flower (in a good position and a larger
surface area for trapping pollen).
• Seed formation – from the ovule
• Fruit Formation – from the ovary wall (soft and fleshy)
• Seed Dispersal – wind (light); animal internal (bright coloured and juicy); animal external
(hooked); self- explosive (bursts open).
Asexual Reproduction
• Also called Vegetative Propagation.
• New plants are formed from a single parent plant (no sex cells or fertilisation).
• The offspring are genetically identical to the parent.
• Runner – a new plant develops at the end of a stem called a runner (spider plant)
• Tuber – use of old tuber to provide energy for the growth of a new plant and other tubers
(potato).
• Advantages – young plant has its own food store; young plant produced in a suitable
environment; no pollination.
• Disadvantages – competition with parent plant; inherited all characteristics from parent so if
a disease kills the parent ⇒ death.
Artificial Propagation
• An artificial way to reproduce a plant asexually.
• Cuttings – small section of the plant allowed to grow roots and then into a new plant.
• Grafting – joining two cut surface of plants (usually to get a combination of good
characteristics).
• Clone – an identical copy.
Transport Systems
• All living plants need water and sugar to stay alive.
• Phloem – sugar transport in all directions. The tissue is alive.
• Xylem – the transport of water (and minerals) upwards only. Xylem is dead. Xylem contains
lignin, which is responsible for providing support.
Plant
1)
2)
3)
4)
5)
6)
7)
8)
Structure
waxy cuticle – waterproof to stop water evaporating
upper epidermis – top layer, allows light through.
palisade mesophyll – photosynthesis (contains chloroplasts)
leaf vein – xylem and phloem
spongy mesophyll - photosynthesis (contains chloroplasts)
air spaces – between spongy mesophyll and allows gas exchange
stomata – pores to allow entry and exit of gases and water loss (most on lower surface)
guard cells – change shape to control entry and exit of gases, (close in dark or when
loosing too much water).
Testing a leaf for Starch
1) boil leaf in water (bursts cell membranes)
2) place leaf in alcohol ( dissolves chlorophyll, removing the green colour)
3) Put leaf in warm water (softens it)
4) Test with iodine solution (blue – black colour = starch).
• Limiting Factors – a factor that holds up the process of photosynthesis because it is in short
supply ( light intensity, carbon dioxide concentration, temperature).