SNAB Biology Unit 2 Topic 4 Key Points

Everything you need to know for the Topic 4 part of the Unit 2 exam.

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Key Terms

A species is a group of organisms with similar morphology, physiology, and behaviour, which can interbreed to produce fertile offspring, and which are reproductively isolated (in place, time or behaviour) from other species.

Sometimes two species are reclassified and merged into one species. Sometimes one species is reclassified and split into two species.

Modern techniques, such as DNA analysis, are often used to identify species. However, DNA cannot always give a clear definition of whether things are the same species as it does not show if two organisms can breed to produce fertile offspring.

Morphology - the outside structure and form of an organism.

Physiology - internal make-up

Behaviour - the way they act

Reproductive isolation - cannot interbreed with each other for some reason.

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A niche is how an organism uses its environment.

Habitat - the place where an organism lives.

Population - a group of interbreeding individuals of the same species found in an area.

Community - the various populations in an area.

Endemic/Endemism - native to an area.

Species Richness - count the number of species in an ecosystem/area. Measures the distribution of species in an area.

Species Evenness - count the number of each species in an area. Measures the abundance of species in an ecosystem.

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Adaptations can be:
Behavioural - actions
Anatomical - parts we can see when we disect.
Physiological - internal workings

Natural selection - the mechanism (first proposed by Darwin & Wallace) by which organisms change over time as they adapt to their changing environments.

Survival of the fittest - individuals who, by chance, posses some characteristic which gives them an advantage over others, will be more likely to survive.

Evolution -  change in form (or behaviour, or physiology) over generations.

Gene pool - consists of all the alleles of all the genes present in a population.

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Taxonomy - classification (placing organisms in groups based on shared features).

There are 5 kingdoms which organisms can be grouped into:

1. Animalia Kingdom: multicellular eukaryotes that are heterotrophs.

2. Plantae Kingdom: multicellular eukaryotes that are autotrophs.

3. Fungi Kingdom: multicellular eukaryotes that are heterotrophs; which absorb nutrients from decaying matter after external digestion.

4. Protoctista Kingdom: eukaryotes that photosynthesis or feed on organic matter from other sources but are not included in other kingdoms. Includes single celled protozoam such as Amoeba.

5. Prokaryote Kingdom: prokaryotic organisms, including bacteria.

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The classification system is made up of seven stages.

Kingdom --> Phylum --> Class --> Order --> Family --> Genus --> Species

Carolus Linnaeus came up with the bionomial system of classification, which is still in use today, where each species is given two Latin names. The first latin name is the genus, the second is the species e.g. Homo sapiens.

The traditional method of classification involved sorting organisms though their kingdom, phylum etc.

The modern method of classification is called the Tree of Life, made up from 3 domains. These domains (branches) are Bacteria (prokaryotes), Archaea (microbes that live in extreme environments), and Eucarya (eukaryotes). This method was proposed in 1990 by Woese, Otto Kandler and Mark Wheelis.

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  • Made up of amylose and amylopectin
  • Amylose is a straight chain coiled into a spiral and amylopectin is the same but with side branches.
  • Starch is made up of 70-80% amylopectin and 20-30% amylose.
  • The compact spiral structure and insoluble nature makes it a good storage molecule.
  • Does not diffuse across cell membranes.
  • Has little osmotic effect within cells.
  • Has 1,4 and 1,6 glycosidic bonds.
  • Used as a storage molecule in plants.

Starch is made up of alpha-glucose molecules joined together by a condensation reaction.

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  • The cell wall of plant cells is made up of cellulose.
  • Cellulose microfibrils weave over each other.
  • The crosslinked cellulose is known as microfibrils.
  • Cellulose only has 1,4 glycosidic links.

Cellulose is made up of beta-glucose molecules joined together. One of the beta-glucose molecules is flipped upside down so that the condensation reaction can happen.

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Vascular Bundle

The stem contains tubes:
1. Xylem - transports water
2. Phloem - transports products from photosynthesis (e.g. glucose).

Vascular bundle in stem = xylem & phloem (sclerenchyma fibres at edge of vascular bundle).

- transports water
- tubes
- large cells with thick walls
- waterproofed with a polymer - lignin. This impregnates the cellulose wall meaning that entry of water and solutes is restricted (cells become lignified).
- The tonoplast breaks down and there is autolysis of cell contents. The cell organelles, cytoplasm and cell surface membrane are broken down by enzymes and lost, leaving an empty tube.
- The end walls between the cells in the columns become lost or highly perforated causing long tubes to form.
- Cellulose microfibrils and lignin in the cell walls give the xylem vessels great strength.

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Water moves through osmosis in the root hair cells. In the xylem, adhesion and cohesion forces cause water to move up the tubes.

Hydrogen bonds keep water moving up the stem (adhesion). They also maintain a continuous stream of water (cohesion).

Tonoplast - the membrane around the vacuole
Amyloplast - storage molecule in cell cytoplasm for starch grains.
Transpiration - movement of water through a plant.
Adhesion - the hydrogen bonds between water and the xylem wall.
Cohesion - hydrogen bonds between the water molecules in the xylem.

Mass flow - bulk flow transportation of substances at an equal rate. In plants, there is mass flow of water and dissolved ions in zylem tubes.

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Mineral Ions & Plants

Nitrate ions - to make amino acids, chlorophyll, nucleic acids, ATP and some growth substances.

Magnesium - to make chlorophyll.

Calcium - growth; structure of cell wall; permeability of cell membrane.

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Drug Testing Procedure

It typically takes 10-12 years and $1 billion to develop a drug.

1. Pre-clinical testing: animal studies and labatory studies on isolated cells and tissue cultures.
2. Clinical Trials (Phase 1): A small group of volunteers are told about the drug and given different doses. Normally uses healthy volunteers. Effects of different doses are monitered.
3. Clinical Trials (Phase 2): 100-300 patients with the disease are tested to look at the drug's effectiveness.
4. Clinical Trials (Phase 3): a large group of patients are split into two groups. One group is given the placebo and the other group is given the new drug. A double-blind randomised controlled trial is when neither the patient nor the doctor know who is recieving the placebo. The results are recorded to see if the new drug is better than the old drug/no drug.
5. After licensing: trials continue to test the safety and effectiveness of the drug.

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Seeds are adapted to ensure they:
- protect the embryo
- aid dispersal
- provide nutrition for the new plant

In flowering plants the ovule is fertilised by the nucleus from a pollen grain and develops into the seed.

The outer layers of the ovule become lignified forming a tough seed coat which protects the embryo within the seed. The surrounding ovary develops into the fruit, which often has an important role in seed dispersal.

In some species the stored food in the seed remains outside the embryo in storage tissue called endosperm. This is common in monocotyledons e.g. cereals. Seeds of this type are called endospermic. In many dicotyledons the embryo absorbs the stored nutrients from the endosperm and the food is stored in the seed leaves (cotyledons) which swell to fill the seed. In some seeds, including Brazil nuts, there are no apparent cotyledons and the food is stored in the hypocotyls, the developing stalk.

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When conditions are suitable and any dormancy has been broken, the seed takes in warer through a small pore in the seed coat. Absorbing water triggers metabolic changes in the seed. Production of plant growth substances is "switched on" and these cause the secretion of enzymes that mobilise the stored food reserves. Maltase and amylase break the starch down into glucose which is converted to sucrose for transport to the radicle and plumule. Proteases break down the proteins in the food store to give amino acids and lipases breakdown the stored lipids to give glycerol and fatty acids.

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Conservation in Seed Banks

Seeds from a variety of endangered plants can be stored in a dormant state in seed banks. Seeds, rather than living plants, are stored because:

  • less space is required
  • most plants produce large numbers of seeds so collecting small samples is unlikely to damage the wild population
  • easier to store because dormant
  • more cost effective

1. Seeds are collected from a number of individual plants.
2. Seeds X-rayed to check for fully formed embryos.
3. Seeds dried to remove water.
4. Seeds stored in the cold (-20C)
5. Seeds periodically germinated to check viability. If less than 75% germinate, those that did germinate are allowed to grow into mature plants that produce their own seeds which are then stored. In 75% or more germinate, the remaining seeds are retained in cold storage and will be checked agian for viability.

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Conservation in Zoos

Roles of zoos in conserving endangered animals:

  • Education (about)
    - illegal trade
    - the need to maintain biodiversity
    - captive breeding programmes
  • Scientific research (including)
    - control of diseases that are reducing populations
    - behavioural studies to further appreciate the needs of animals in captivity.
    - development of techniques to improve breeding success
  • Captive breeding programmes (so that)
    - animal numbers increase, reducing the risk of extinction.
    - some animals can be released to maintain or establish breeding populations.
    - genetic diversity is maintained
  • Reintroduction programmes (which)
    - release captive bred animals back into the wild.
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Problems with captive breeding:

  • reduced genetic diversity
  • reduced chance of adapting to environmental change
  • increased risk of a genetic condition becoming more common in the breeding population

Ways to reduce inbreeding and maintain genetic diversity

  • Do not allow organisms to repeatedly breed with the same partner, possibly isolating partners.
  • Select partners, possibly by adding a potential partner to a cage, IVF or inter-zoo swapping.
  • Keep a record/database of individuals in captivity and their breeding history e.g. stud books, so that choice of partners is controlled.
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these notes are brill thanks




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