Genetic Diversity and Variety of Life Flashcards
Genetic diversity
The greater number of alleles, the more diverse an organism is. This makes it more likely to adapt to a change in their environment.
Selective breeding/ artificial selection
Only breeding individuals with desired characteristics, which reduces genetic diversity. Eg/ cows with high milk production
Founder Effect
A few individuals from a population colonise a new region so they only carry a few of the alleles of the whole original population. Therefore the new population shows less genetic diversity than the first population.
Genetic bottlenecks
A natural disaster or interference by humans reduces a population, meaning less diversity, and therefore less alleles. They are therefore less likely to be able to adapt to changes in their environment.
Haemoglobin Structure
Primary structure: 4 polypeptide chains Secondary structure: Coiled into a helix Tertiary structure: Folded into a precise shape to carry oxygen Quaternary structure: 4 link t form a near spherical molecule. Each is associated with a haem group containing an Fe2+ ion. Each ion can combine with an O2 molecule, so each haemoglobin can carry 4 O2 molecules.
Role of haemoglobin
Readily associate with oxygen at the gas exchange surface. Readily dissociate with oxygen at the respiring tissues.
Environmental factors
In an environment with little oxygen, the haemoglobin must readily combine with oxygen. This means that it will not release it as readily, but this is not a problem with a low metabolic rate. An organism with a high metabolic rate needs to release oxygen into tissues readily. As long as there is lots of oxygen in its environment it is most important to have a haemoglobin which readily releases oxygen.
What causes a change in affinity?
The presence of carbon dioxide at respiring tissues reduces the affinity of haemoglobin by changing its shape
Bohr effect
Different affinities of haemoglobin comes from different shapes.
Loading and unloading of oxygen
- Carbon dioxide is low at the gas exchange surface because it is being removed
- pH rises due to low carbon dioxide levels, changing the shape of haemoglobin to readily load oxygen
- This also increases affinity so the oxygen is not released while being transported in the blodd
- Carbon dioxide is produced by respiring cells in the tissues
- Carbon dioxide is acidic in solution, so it lowers the pH
- Haemoglobin changes into a shaoe with low oxygen affinity
- The oxygen is released into the respiring tissues
Oxygen dissociation curves
A shift to the left shows increased affinity, while to the right shows decreased affinity.
An animal in a low oxygen environment will have a curve to the left, because they must associate with as much oxygen as possible. The same is true of animals with a small SA:Volume ratio or who don’t move much because they have low CO2 levels in their cells.
Animals with a large SA:Volume ratio, such as mice, have a curve to the right as they respire lots to keep warm.
Starch
A polysaccharide found in plants as small grains. \plentiful in seeds and storage orgas eg/ potato tubers. It is never found in animal cells. The major energy source n most diets.
Chains of α-glucose monosaccharides linked by glycosidic bonds formed by condesation reactions. The unbranched chain is wound into a tight coil- making it vey compact. It stains blue with iodine solution. Its main role is energy storage which it is suited for because:
- Insoluble so it doesn’t draw water into cells by osmosis, nor does it diffuse out of cells easily
- Compact to maximise storage
- Froms α-glucose when hydrolised which is easily transported and used in respiration
Glycogen
Structurally similar to starch, but made of shorter, more highly branched chains. Suited to function for the same reasons as starch, but is even more readily hydrolised.
Cellulose, structure and function
Made of ß-glucose, which forms straight unbranched chains. These run parallel to each other and hydrogen bonds form cross links. The quantity of these hydrogen bonds helps make cellulose so strong.
The molecules are grouped together to form microfibrils which are then arranged in parallel groups called fibres.
Provides rigidity to cell walls and exerts and inward pressure to prevent the cell bursting when water enters. This gives rigidity to the stem and leaves.
Turgidity provides maximimum area for photosynthesis.
Palisade leaf cells
- long and thin to absorb sunlight
- chloroplasts to collect maximum sunlight
- vacuole pushes cytoplasm and chloroplasts to the edge of the cell
Chloroplast structure
- Typically disc shaped, approximately 2-10 µm long and 1 µm wide in diameter
- Chloroplast envelope is a highly selective double plasma membrane
- Grana are stcks of up to 100 thylakoids which contain chlorophyll. Some thylakoids have intergranal lamella which joing them to an adjacent grana. Site of the first stage of photosynthesis.
- Stroma is a fluid filled matrix and the site of the second stage of photosynthesis
Chloroplast adaptations
- Large surface area provided by granal membranes for the attachment of chlorophyll, electron carriers and enzymes for the first stage of photosynthesis. They are attached in a highly ordered fashion
- Stroma fluid contains all enzymes necessary for the second stage of photosynthesis.
- Contain DNA an ribosomes to quickly and easily make some of the proteins for photosynthesis
Cell wall features and functions
Features:
- Consist of a number of polysaccharides including cellulose.
- Cellulose microfibrils are embedded in a matrix
- A thin layer called the middle lamella marks the boundary between adjacent cell walls, and cements them together.
Functions:
- Provide mechanical strength to the cell, preventing it from bursting under the pressure created by the osmotic entry of water
- Mechanical strength to the plant as a whole
- Allow water to pass thorugh it, contributing to water movement through the plant
Differences between plant and animal cells
Plant:
- Cell wall and cell membrane
- Large quantities of chloroplasts present in most cells
- A large, single central vacuole fille with cell sap
- Starch used for storage
Animal
- No cell wall
- No chloroplasts
- If vacuoles ae present, they are small and scattered throughout the cell
- Glycogen used for storage
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