Plant Structure and Function, Biodiversity and Conservation flashcards

Topic 4: Plant Structure and Function, Biodiversity and Conservation

Middle lamella, pits and plasmodesmata

Middle lamella: pectin-rich layer that cements neighbouring cells together. Pits: thin areas of wall with no secondary thickening, for movement of water and solutes. Plasmodesmata: membrane-lined channels through walls linking cytoplasm.

Amyloplast vs chloroplast

Both have a double membrane and starch grains. A chloroplast has grana and chlorophyll and carries out photosynthesis; an amyloplast has no chlorophyll and stores starch.

Why are cellulose chains straight, and how do they give strength?

Every second β-glucose is turned upside down so the –OH groups line up for β-1,4 glycosidic bonds. Parallel chains are held by many hydrogen bonds into microfibrils with high tensile strength.

Sclerenchyma fibre vs xylem vessel vs phloem sieve tube

Sclerenchyma: dead, thick lignified wall, narrow empty lumen; support. Xylem vessel: dead, lignified with pits, wide lumen, no end walls; support plus water and ions. Sieve tube: living, thin unlignified wall, sieve plates; translocation.

Roles of nitrate, calcium and magnesium ions in plants

Nitrate: nitrogen for amino acids, proteins, nucleotides and chlorophyll. Calcium: calcium pectate in the middle lamella; membranes; cell division. Magnesium: at the centre of chlorophyll; enzyme activator.

Why measure dry mass in a mineral deficiency investigation?

Fresh mass changes with water content; dry mass measures the biological material actually made.

Tensile strength of a plant fibre

Tensile strength = breaking force ÷ cross-sectional area (Pa). Force F = m × g (g = 9.81 N kg⁻¹); area A = π(d/2)². Keep length, moisture and loading rate the same; measure the diameter in several places.

Plant-derived drugs: give four examples

Foxglove: digoxin (heart conditions). Cinchona: quinine (malaria). Sweet wormwood: artemisinin (malaria). Willow: salicylic acid, from which aspirin was developed (pain relief).

Testing plant extracts for antimicrobial activity

Spread bacteria on nutrient agar to make a lawn; add sterile discs soaked in extracts, with a solvent-only disc (negative control) and an antibiotic disc (positive control). Incubate and compare clear zone areas, π(d/2)².

Placebo and double-blind trials

A placebo looks identical but has no active ingredient, controlling for expectation. In a double-blind trial neither patients nor the staff treating or assessing them know who has which, reducing bias.

Phases 1, 2 and 3 of drug testing

Phase 1: a few healthy volunteers; safety, side effects, dose range. Phase 2: a small number of patients; effectiveness and dose. Phase 3: a large number of patients; compared with a placebo or existing treatment.

Endemism and niche

Endemism: a species found naturally only in one geographical area. Niche: how a species fits into its ecosystem: habitat, food, relationships with other species and active period.

Index of diversity (D) for counts of 6, 3 and 1

D = N(N − 1) ÷ Σn(n − 1). N = 10, so N(N − 1) = 90. Σn(n − 1) = 30 + 6 + 0 = 36. D = 90 ÷ 36 = 2.5. A higher D means greater diversity.

Heterozygosity index

Number of heterozygotes ÷ number of individuals in the population. Higher means more genetic diversity. Example: 4 heterozygotes in 25 animals = 0.16.

How did molecular evidence lead to the three-domain system?

Comparison of ribosomal RNA sequences split organisms into Archaea, Bacteria and Eukarya. Fewer sequence differences mean a more recent common ancestor. New groupings are evaluated by publication, peer review and repetition.

Zoos and seed banks: one strength and one weakness each

Captive breeding in zoos: safe from wild threats and planned matings protect heterozygosity, but small populations lose genetic diversity. Seed banks: many species and alleles stored cheaply, but some seeds cannot be dried and frozen, and habitats are not conserved.