SRMJEEE Biology (Botany) Flashcards

24 sample cards from the Biology (Botany) deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What are the two complex tissues and their components?

   Xylem (tracheids, vessels, xylem fibres, xylem parenchyma) for water/mineral conduction; Phloem (sieve tube elements, companion cells, phloem fibres, phloem parenchyma) for food translocation.

2. Name the three tissue systems described by Sachs.

   Epidermal tissue system (epidermis, stomata, trichomes), ground (fundamental) tissue system (cortex, pericycle, pith, mesophyll), and vascular tissue system (xylem and phloem).

3. Differentiate open and closed vascular bundles.

   Open vascular bundles have cambium between xylem and phloem and are capable of secondary growth (dicot stems). Closed vascular bundles lack cambium and cannot undergo secondary growth (monocot stems).

4. What is secondary growth and which meristems bring it about?

   Secondary growth is the increase in girth (thickness) of stems and roots due to the activity of two lateral meristems: the vascular cambium (produces secondary xylem and phloem) and the cork cambium (phellogen).

5. What are annual rings (growth rings) and how do they form?

   Annual rings are concentric rings of secondary xylem formed by the differing activity of cambium in favourable (wide, light early/spring wood) and unfavourable (narrow, dark late/autumn wood) seasons; counting them estimates a tree's age (dendrochronology).

6. Distinguish heartwood from sapwood.

   Heartwood (duramen) is the central, dark, dead, non-conducting secondary xylem filled with tannins and resins providing mechanical support; sapwood (alburnum) is the peripheral, lighter, living xylem that actively conducts water and minerals.

7. What is the bark and what are its components?

   Bark is all tissue exterior to the vascular cambium — it includes the secondary phloem, cork cambium (phellogen), cork (phellem) and secondary cortex (phelloderm). Lenticels in the cork allow gas exchange.

8. Define diffusion and state two factors affecting its rate in plants.

   Diffusion is the net movement of molecules/ions from a region of higher concentration to lower concentration along a concentration gradient, without expenditure of energy. Rate increases with steeper concentration gradient, higher temperature, and smaller molecule size/pressure.

9. Define osmosis and the role of the semipermeable membrane.

   Osmosis is the net movement of solvent (water) molecules from a region of higher water potential (dilute/pure water) to lower water potential (concentrated solution) across a selectively (semi) permeable membrane.

10. Write the equation relating water potential, solute potential and pressure potential.

    $$\Psi_w = \Psi_s + \Psi_p$$ where $\Psi_w$ is water potential, $\Psi_s$ (or $\Psi_\pi$) is the solute (osmotic) potential, and $\Psi_p$ is the pressure potential.

11. What is the water potential of pure water at standard temperature and pressure, and what sign does solute potential always carry?

    The water potential of pure water at standard conditions is zero ($\Psi_w = 0$). Solute (osmotic) potential is always negative ($\Psi_s < 0$), since adding solute lowers water potential.

12. Define plasmolysis and the condition under which it occurs.

    Plasmolysis is the shrinkage of the protoplast away from the cell wall when a cell is placed in a hypertonic solution (external solution has lower water potential), causing water to exosmose out of the cell.

13. Define transpiration and name its three types.

    Transpiration is the loss of water in the form of vapour from the aerial parts of a plant. Types: stomatal (~90%, through stomata), cuticular (through the cuticle) and lenticular (through lenticels).

14. According to the cohesion-tension theory, what forces drive the ascent of sap?

    Transpiration pull created at the leaf surface, transmitted down a continuous water column held together by cohesion (water-water hydrogen bonding) and adhesion (water-xylem wall attraction); this transpirational pull is the main driving force for the ascent of sap.

15. What is the role of guard cells in stomatal opening, and what ion is key?

    Stomata open when guard cells become turgid: an influx of $\ce{K+}$ ions lowers water potential, water enters by osmosis, and the unevenly thickened guard cells bow outward opening the pore; loss of $\ce{K+}$ and water closes them.

16. What are the criteria for an element to be called an 'essential element'?

    An element is essential if: it is absolutely necessary for normal growth and reproduction, it is directly involved in plant metabolism, its deficiency cannot be met by another element, and its absence prevents the plant from completing its life cycle.

17. Differentiate macronutrients and micronutrients with examples.

    Macronutrients are required in large amounts (>10 mmol/kg dry matter): C, H, O, N, P, K, Ca, Mg, S. Micronutrients (trace elements) are needed in small amounts (<10 mmol/kg): Fe, Mn, Cu, Zn, B, Mo, Cl, Ni.

18. Why is nitrogen, phosphorus, potassium and magnesium deficiency seen first in older leaves?

    Because N, P, K and Mg are highly mobile elements that are readily remobilised from older (senescing) leaves to young growing tissues; thus their deficiency symptoms appear first in mature/older leaves.

19. Name the element whose deficiency causes chlorosis appearing in young leaves first, and explain why.

    Iron (and also calcium, sulphur, boron, copper) deficiency shows in young leaves first because these elements are relatively immobile and cannot be remobilised from older tissues to the growing apices.

20. What is chlorosis and which nutrient deficiencies cause it?

    Chlorosis is the loss/yellowing due to reduced chlorophyll. It results from deficiency of N, K, Mg, S, Fe, Mn, Zn and Mo (Mg and Fe are central to chlorophyll synthesis).

21. What is biological nitrogen fixation and which enzyme catalyses it?

    Biological nitrogen fixation is the reduction of atmospheric dinitrogen to ammonia by living organisms, catalysed by the enzyme nitrogenase: $$\ce{N2 + 8H+ + 8e- + 16ATP -> 2NH3 + H2 + 16ADP + 16Pi}$$

22. Write the overall steps of nitrification in the soil.

    Nitrification is the oxidation of ammonia to nitrate by soil bacteria: $$\ce{2NH3 + 3O2 -> 2NO2^- + 2H+ + 2H2O}$$ (by Nitrosomonas), then $$\ce{2NO2^- + O2 -> 2NO3^-}$$ (by Nitrobacter).

23. What is the symbiotic nitrogen-fixing bacterium of leguminous root nodules, and what pigment protects nitrogenase from oxygen?

    Rhizobium forms a symbiosis with legume roots, inducing root nodules. The pink pigment leghaemoglobin acts as an oxygen scavenger, protecting the oxygen-sensitive nitrogenase enzyme.

24. What is the role of GS-GOGAT in nitrogen metabolism (fate of ammonia)?

    Ammonia produced by fixation/reduction is assimilated into amino acids: glutamine synthetase (GS) combines ammonia with glutamate to form glutamine, and glutamate synthase (GOGAT) transfers the amide group to 2-oxoglutarate forming two glutamates; amino acids are then made by transamination.

What this deck covers

Biology (Botany) flashcards FAQ