BIOL 2390 - Topic 6 (part 4)

Thermal balance

Plants and animals must maintain thermal balance in order to maximize energy use, cellular function, and biochemical efficiency

Heat is gained by…

1.) Solar radiation

2.) Conduction (transfer of heat from one object to another)

3.) Cellular respiration

Heat loss occurs by…

1.) Convection (heat transferred from movement of fluids)

2.) Evaporation (i.e. transpiration)

Poikilotherms

A variable body temperature that is similar to the environment

Homeotherms

The maintenance of a constant body temperature, regardless of the environment

Ectotherms

Organisms that generate heat primarily from the external environment (such as the sun)

Endotherms

Organisms where heat is generated primarily by metabolic processes (such as cellular respiration)

Ectotherms and endotherms vs. poikilotherms and homeotherms

Ectotherms are usually poikilotherms and endotherms are usually homeotherms, but there are times where endotherms are more like poikilotherms and ectotherms are more like homeotherms

Plant thermal balance

It occurs within the leaves, to maintain optimal temperatures for photosynthesis

Temperature effect on photosynthesis/respiration

1.) At high temperatures, respiration exceeds photosynthesis

2.) Therefore, it is important that plant temperatures stay within 20-25ºC, which maximizes the gains of photosynthesis and minimizes the loss from respiration

Plants lose heat via…

Evaporation cooling and convection to the air around the leaf

Boundary layer formation

The layer of heat and moisture adjacent to the surface of the leaf, as a result of the loss of water and heat from the leaf

Thickness of boundary layer

The thicker the boundary layer, the slower the loss of water and heat (i.e. we are able to conserve more water and lose less heat)

Trade-offs for water loss and heat dissipation from the boundary layer

1.) It does not affect CO2 absorption

2.) But it does reduce its ability to dissipate heat

The boundary layer is modified by…

1.) Wind

2.) Leaf size/shape

Wind effect on boundary layer

It reduces the size of the layer, by causing the mixing of air, blowing the layer away due to turbulence

Leaf size/shape on boundary layer

It influences the dynamics of air flow and the size of the boundary layer

Leaf size/shape on boundary layer (effect)

1.) The larger and smoother leaves, the thicker and more stable the layer

2.) The smaller, more convoluted the leaves, the thinner and less stable the layer

Leaves with thicker boundary layers are commonly found in…

They’re commonly found in shaded plants or lower canopy leaves, where heat is not an issue

Leaves with thinner boundary layers are commonly found in…

It is commonly found in full sun plants or upper canopy leaves, because it meets more light/heat and therefore not want the heat to build up

Plants that have large leaves at the bottom and small leaves at the top display…

It displays phenotypic plasticity