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Chapter 17 Variation and Selection - Coggle Diagram
Chapter 17 Variation and Selection
17.1 Variation
Discontinuous Variation
Variation in which there are distinct categories of phenotype with no intermediates
Blood groups
Eye colour
Hair colour
Continuous Variation
Variation in which there is a continuous range of pehnotypes between two extremes
Height
skin colour
Causes of variation
Different genotypes
Environment
Mutation
random change in a gene, which can produce new alleles; mutation incolves change in the base sequence in DNA
17.2 Selection
Adaptive features
An inherited feature that helps an organism to survive and reproduce in its environment
Xerophytes
Thick waxy cuticle (prevents evaporation)
Sunken stomata (traps humid air in pits)
Spines / reduced leaves (minimizes surface area)
Surface hairs / trichomes (reflects heat & traps moisture)
Rolled leaves (shelters stomata from wind)
Succulent tissues (stores water in stems/leaves)
Photosynthetic stems (takes over food production)
Extensive shallow roots (absorbs surface dew & rain)
Deep taproots (reaches underground water tables)
Hydrophytes
Thin or absent waxy cuticle (water loss is not an issue; allows direct absorption)
Stomata on upper epidermis (allows floating leaves to exchange gases with the air)
Always-open stomata (transpiration is not restricted since water is abundant)
Aerenchyma tissue (spongy packaging cells with large air spaces for buoyancy)
Internal gas reservoirs (traps oxygen and carbon dioxide for floating and respiration)
Reduced root systems (roots are primarily for anchorage, not water absorption)
Feathery or highly divided submerged leaves (creates large surface area for gas exchange)
Flexible stems and leaves (bends easily with water currents to prevent snapping)
Little to no xylem tissue (no need for specialized internal water transport tubes)
Large, flat floating leaves (maximizes sunlight capture on the water surface)