Biology - Unit 2 Topic 4

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  1. Compare the ultrastructure of plant cells with that of animal cells.
    • Both eukaryotic cells.
    • Cell Walls:
    • Plant cells have a cell wall made of cellulose fibrils and pectin cross linked. It strengthens the cell and allows it to be turgid without bursting.
    • Amyloplasts:
    • Plant cells have amyloplasts (membrane bound) which contain starch - food source.
    • Chloroplasts:
    • Site of photosynthesis. Present in plants, not animals. They contain chlorophyll.
    • Image Upload 1
    • Vacuole:
    • Membrane bound organelle which contains water and dissolved substances. Helps maintain turgor.
    • Tonoplast:
    • Vacuolar membrane.
    • Plasmodesmata:
    • A junction between adjacent cells, which links one cytoplasm to the next. Used for intercellular communication.
    • Pit:
    • The area where plasmodesmata can form or has previously formed.
    • Middle lamella:
    • Pectin 'glue' which attaches two cell walls together.
  2. Compare the structure and function of starch and cellulose. Explain role of hydrogen bonds in formation of microfibrils.
    • Cellulose is a polysaccharide made of β-glucose which is joined through a condensation reaction forming glycosidic bonds. 
    • Alternating glucose molecules are inverted forming hydrogen bonds between hydroxyl group and oxygen atom in between chains (cross-linking).
    • Cellulose chains are straight and unbranched, therefore they can be packed close together, strengthening the H bonds.
    • Cellulose chains are packed together into microfibrils.
    • Microfibrils wind around each other to form fibres.
    • Layers of fibres forms cell wall.
  3. Explain how the arrangement of microfibrils and secondary thickening contribute to physical properties of plant fibres.
    • 1. Cellulose microfibrils and matrix build up on either side of middle lamella.
    • 2. Primary cell wall: First to form, cellulose microfibrils laid down is the same direction.
    • 3. Secondary cell wall: As the plant ages, the microfibrils are laid down at right angles to those in the primary wall. Strengthens cell wall.
    • 4. In some plants cell walls are lignified. This strengthens the walls further. Long cells with cellulose walls that have been lignified are known as plant fibres.

    Plant fibres are extracted and used for many things, e.g rope, clothes, paper
  4. Compare the position and function of schlerenchyma and xylem.
    Image Upload 2

    • Xylem vessels are on the inside of the vascular bundle. They transport water and minerals.
    • Sclerenchyma is found on the cap of the vascular bundle. It is the fibrous cap. It is used for support of the stem.
    • Collenchyma is found below the epidermis. Used for support and packing.
    • Parenchyma (unspecialised cells) is found right in the middle. It is packing tissue.
  5. Compare the structures and features of sclerenchyma and xylem.

    • Tissue found surrounding vascular bundle.
    • Have strong secondary walls, and sometimes form fibres.
    • These fibres can be lignified in a spiral or ring patters, making fibres strong but flexible.
    • When they are completely impregnated with lignin → form sclereids.


    • Xylem starts off as living tissue - protoxylem.
    • Once the cells develop they change from living vessels to non-living tubes of lignin.
    • Water moves out from pits.
  6. Identify sclerenchyma and xylem under a light microscope.
    Image Upload 3


    Image Upload 4

    Xylem (far left)
  7. Explain the importance of water and inorganic ions to plants.
    • Nitrate
    • Used to make amino acids, to make proteins.
    • When they lack →
    • Growth is stunted
    • Old leaves turn yellow & die.
    • Calcium
    • Combine with pectin to form calcium pectate (cell wall).
    • Permeability of membranes.
    • When they lack →
    • growing points die
    • leaves turn yellow and crinkly
    • Fruit grows inwards and rots
    • Magnesium
    • Needed to produce chlorophyll
    • When they lack →
    • yellow areas develop on older leaves
    • growth slows down
  8. Describe how plant fibres and starch may contribute to sustainability.
    • They are sustainable/renewable. Meaning that they can be replaced/replanted. Are not a limited resource.
    • They are carbon neutral. Even though they release COthey take it back in when replanted.
    • They are biodegradable. e.g bio-plastics.
    • Plant fibres →
    • high tensile strength, clothes, building.
    • Plant oils →
    • Bio fuels.
    • Starch →
    • Packaging, food, absorbants, glues...
  9. Compare historic drug testing with contemporary drug testing.
    • William Withering treated dropsy patients with different doses of foxglove. He worked out the correct dose by seeing when patients would become ill. Through this procedure he also accidentally killed someone. This is now considered unethical and as a violation of clinical trial practice.
    • Clinical Trial Procedure:
    • Pre-clinical testing →
    • Drug tried on cultured cells and animals to see effect.
    • Clinical Trials, Phase 1
    • Small group of healthy volunteers given different doses of drug. Safe dosage, side effects and reactions to drug are noted.
    • Phase 2 →
    • Small group of patients (with disease) are given drug. Optimum dose and reactions are noted.
    • Phase 3 →
    • Large group of patients are given drug. Patients randomly divided in 2 groups. Some patients given placebo in double blind trial. Results analysed. If drug has positive effect it is put forward for licensing.
  10. Describe the concept of niche and examples of adaptations to environment.
    • Niche
    • A specific part of the ecosystem in which a species lives and any adaptations the species has to make it successful.
    • Adaptations can be:
    • Behavioural
    • The way a species behaves to improve its chance of survival. e.g. Mating calls.
    • Physiological
    • Processes inside an organism's body that increase its chance of survival. e.g. hibernation.
    • Anatomical/Structural
    • Structural features of an organism's body that increase its chance of survival. e.g. Rabbits brown fur to mimitize.
  11. Describe how natural selection can lead to adaptation and evolution.
    • Natural selection = 'survival of the fittest'.
    • Predation, disease, and competition create a struggle for survival.
    • Better adaptations = more likely to survive and pass on genes.
    • Number of advantageous genes increases over time.
    • Over generation this leads to evolution.
    • E.g. The peppered moth.
  12. Discuss the process and importance of critical evaluation of new data by the scientific community, which leads to new taxonomic groupings.
    • Seven taxonomic groups.
    • Kingdom
    • Phylum
    • Class
    • Order
    • Family
    • Genus
    • Species
    • Originally taxonomic grouping was based on morphological and physiological similarities.
    • New technology based on molecular phylogeny has caused new groupings of species.
    • Analysis of DNA and RNA allows to see how closely related organisms are. 
    • A third domain was discovered through analysis of molecular phylogeny. It was found that archaea are more closely related to eukaryotes that to bacteria
    • This suggested a common ancestor.
  13. Explain the terms biodiversity and endemism and describe how biodiversity can be measured within a habitat using species richness and within a species using genetic diversity.
    • Biodiversity:
    • Variety of living organisms in an area
    • Endemic:
    • When a species is found only in a particular niche in a particular ecosystem.
    • Species richness:
    • The number of species in an area/location.
    • Measured by →
    • Indicator species (used to indicate health of ecosystem)
    • Keystone species, crucial species (used to measure the health of ecosystem)
    • Quadrants (plants), sweepnets (flying insects), pitfall traps (land insects).
    • Genetic diversity:
    • Measure variety of different alleles within the gene pool, analysing DNA. The greater the diversity, the more biodiversity.
  14. Discuss and evaluate the methods used by seed banks in the conservation of endangered species and their genetic species.
    • Seed banks
    • Store seeds from endangered plants.
    • Seeds of different sizes/plants are stored to ensure genetic diversity.
    • Seeds are dried, sterilised and placed in low temperatures and dry conditions.
    • Their viability is tested every now & again and replanted to put new seeds back into storage.
    • ☑Seeds can be reintroduced to the wild if conditions are appropriate.
    • ☑Can be used to grow endangered plants used for medicine.
    • ☒Only studying seeds limits the data to a small population. Information may not be representative.
    • ☒Testing and storing seeds is expensive.
    • ☑Cheaper than storing fully grown plants.
    • ☑Seeds are more likely to survive longer
  15. Describe how to determine tensile strength of plant fibres practically.
  16. Describe how to investigate plant mineral deficiencies.
  17. Describe how to investigate the antimicrobial properties of plants.
  18. Discuss and evaluate the methods used by zoos  in the conservation of endangered species and their genetic species.
    • Zoos use captive breeding programs.
    • Stud books, surrogate mothers and genetic testing is used to ensure genetic diversity.
    • If species reproduces enough it can be reintroduced into wildlife.
    • ☒Reintroduction may fail.
    • ☒Unethical to keep animals in captivity.
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Biology - Unit 2 Topic 4
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