2a. The Phusical Enviornment Flashcards
Light
Too little light = gain from photosynthesis does not cover energy requirements = for example the forest floor
Too much = excess light can not be absorbed as energy and photo damage can occur.
Adaptation to light levels
May be permanent (morphology of plants) or dynamic (chloroplast moving in leaf cell)
Life history adaptations
Shade tolerant plants almost always perennial, as an annual life cycle requires high energy
Germination
Lightbkevels drive germination success. Some require light, some darkness => plants at the bottom of the forest will develop and reproduce before tree grow leaves and block the light and temperature correlated
Poikilotherms
Pants => generally assume the temperature of their environment
Hemeotherms
Maintain steady body temperature
Extreme body temperatures can cause metabolic difficulties and physical damage.
E.g. Forest damage = burnt tips
Cardinal points of temperature tolerance
- Cold death
- Cold rigidity
- Range pf active life
- Health rigidity
- Heat death
Frost avoidance
Annual life cycles, over wintering as seeds - Deciduous trees lose frost sensitive leaves during winter
Frost tolerance
Supercooling (reduce freezing threshold below 0 degrees), loss of water to extra cellular areas to avoid cell damage.
Thermal insulation to avoid short term freeze events
Heat avoidance
Division of leaves, hairy leaves reflect radiation, position of leaves (similar to light adaptation), transpiration cooling n
Heat tollerance
Hardening (chemical processes in cell membrane to increase resistance to heat stress
Psychrophiles
Adapted to cold.
Themophiles
Require high temperature
Extremephiles
Slow ice algae
Mesophiles
Most plants prefer medium temperatures
Pyrophytes
Fire dependent for seed opening
Temperature
Not all life cycles require the same temperature. Some plants can regulate temperature => sunflowers follow the sun. Distribution of plants depend on temperature. Each plant needs to have perfect conditions to reproduce
Water and animals
Mammals can withstand water loss of about 10% of their body water
Water can be lost through skin, respiration, excrement and other secretions.
The level of water lost amongst animals is dependent on climate conditions
Majority of terrestrial animals are dependent on water sources such as rivers, while some animals take up water through their food
Water and plants - transpiration is controlled by:
Waxy cuticle
Stomata opening
Lenticles ( waxy small leaf in drier climates)
Water stress
Water loss relatively high compared to absorption through roots. Reduces rates of photosynthesis
I.e. = closing of stomata = lack of gas exchange
Higher vulnerability at seedling stage
Limited water availability is often accompanied with high temperatures and high light levels.
Cells cannot desiccate or rehydrate or take up water from the air.
Plants could only expand into terrestrial habitats with the division of labour between organs
Leaf surface is impermeable to h2o and co2
Algae, mosses and lichens cannot have the division of labour and so cannot desiccate but do the other two
Adaptations to water stress: desiccation avoidance
Survive as dormant seeds, shedding leaves, dormant plants below ground, storage of water in the stem (cacti), reduce transpiration, open stomata at night, salt exclusion,excretion mechanisms
Salt
Atmospheric gradient changes with salinity. Most marine organisms cannot live in fresh water and vice versa.
Salmon for example has adapted to survive in both fresh and salt water
Soils - nutrients
Bounded to soil particles and exchanged with the plant through cation exchange. pH value regulates nutrient availability (best in neutral pH)
Water
Look at slide
Capillary water is mainly what plants can use
Field capacity
How much water the soil can hold. Usually less than 3 days after rainfall
Permanent wilting point
Water content of soil beyond which most plants are no longer able to take up water
Plant available water
Field capacity - wilting point
