BIOL 2390 - Topic 6

Maintaining equilibrium

Organisms must maintain an equilibrium between their internal and external environments, to keep their conditions within a specific range, because cells, organs, and enzymatic processes function within a certain set of limits (i.e range)

Homeostasis

The maintenance of a relatively stable internal environment in a variable external environment, through feedback responses

Homeostasis optimum

There is an optimum, but it is not a fixed value

Homeostasis + sensory mechanisms

Sensory mechanisms triggers physiological and/or behavioural responses

Sensory mechanisms triggering physiological and/or behavioural responses example

Cold = shivering

Hot = sweating

Downside of homeostasis

It can cost a significant amount of energy

Homeostasis vs. organism size

Smaller organisms engage in homeostasis more easily than larger organisms, due to scaling

Scaling

Refers to the fact that bodies change in a predictable way when they get larger, such that they encounter more problems, which is why larger organisms have a harder time engaging in homeostasis

Why do smaller organisms have an easier time with homeostasis

They have a larger surface area to volume ratio, therefore they don’t need complex mechanisms to maintain homeostasis

Why do larger organisms have a harder time with homeostasis

1.) They have a lower surface area to volume ratio

2.) This causes constraints in the diffusion of oxygen, nutrients, carbon, water, and heat.

How do larger organisms overcome their difficulty with homeostasis

They have complex systems in the body, such as the circulatory system, respiratory system, etc

Importance of water

It is essential for life and it is involved in all biological reactions

Cause of loss of water (waste…)

1.) It acts as a medium for waste disposal

2.) Dissipation (i.e. loss of water) removes excess heat

Significance of water loss

It means that an organism must offset these water losses by taking up water from the external environment, in order to maintain water balance

Issues that come with maintaining water balance

Not all environments are equal, as some are drier than others, therefore you have to be careful not lose too much water via evaporation

Varying water loss adaptations

Organisms and species vary in terms of their water loss adaptations

Animals: water loss adaptations

1.) Hair, feathers, scales

2.) Behavioural responses

3.) Kidneys or cloaca

4.) Reduced respiratory losses (i.e. from breathing)

Hair, feathers, and scales as water loss adaptations

It reflects light away, resulting in less heat and therefore less evaporation

Behavioural responses as water loss adaptations examples

1.) Animals: Koala’s hug trees to cool down

2.) Plants: They curl their leaves to prevent water loss

Kidney/cloaca as water loss adaptations

It reduces water loss from excretion/waste disposal

Plants: water loss adaptations

1.) Cuticle + Stomata

2.) Modified leaf morphology (angle their leaves to increase light reflection)

3.) Behavioural responses

4.) Alternate photosynthetic pathways

Stomata

Openings within the leaf tissue that allows gases and water to come in

Water balance in aquatic animals

They face the constant exchange of water with their environment, via osmosis, but the exchange is different depending on whether they are freshwater or marine organisms

Freshwater organisms’ water balance issues

They have a higher solute concentration inside their body, causing them to passively gain water

Marine organisms’ water balance issues

They have a lower concentration of solutes inside their body, causing them to passively lose water.

Freshwater organisms solving water balance issues

It depends on the species, but generally, they limit drinking and undergo constant urination

Marine organisms solving water balance issues

They drink water and then filters out the salt from the seawater (ex., turtles)

Terrestrial animals compensating for water loss

It usually depends on the environment that they are in, as different environments will be drier and others will be more wet

Terrestrial animals compensating for water loss (methods)

1.) Directly drinking water

2.) Obtaining moisture from food

3.) Metabolic production of water

Metabolic production of water

Certain organisms, such as desert rodents, don’t have access to liquid sources, therefore they have to make their own water via cellular respiration

Kidney’s

It recovers water during waste filtration of the bloodstream, reducing the amount of water lost in waste in the process

Kidney parts

1.) Nephron, which is where waste is pushed out

2.) Loop of henle, which is the part that absorbs water

Modified loop of henle

1.) Certain animals, usually those in dry environments like desert rodents, have a longer loop of Henle, which allows for greater water absorption efficiency

2.) This requires minimal energy, but it does require specific selection pressures to be present for the adaptation to develop

Nasal systems that helps with water balance

Nasal evaporators/condensers reduce water loss when exhaling, while also somewhat helping cool desert animals when inhaling?

How nasal evaporators/condensers work

1.) Air temp is cooler than body temp and the exhaled air is warmer than the cool nasal cavity, therefore causing condensation in the nasal passage

2.) This is absorbed in the nasal cavity, resulting in reduced water loss

Nasal evaporators/condensers cooling desert animals?

1.) When air comes in, it goes through well-hydrated passages, therefore causing evaporation

2.) This results in a cooling effect that hydrates the air during inhalation

Plant evolution to variability in environments

Plants have evolved a wide range of responses to the variability of precipitation and soil moisture

Plant adaptations to variable precipitation and soil moisture patterns

1.) Closing their leaf stomata

2.) Intentionally curling or wilting their leaves

3.) Losing their leaves entirely

Closing leaf stomata

It is a good response for short-term water loss, but it can eventually cause more damage if left closed for too long

Closed leaf stomata disadvantages

1.) It can lead to high heat levels

2.) It can’t take in CO2, therefore photorespiration and photodamage eventually occurs

Photo damage

When the light ends up causing damage to the plant, because it can’t carry out photosynthesis (occurs when stomata are closed)

Plants curling or wilting their leaves

It reduces light absorption, by increasing light reflection

Plants losing their leaves entirely

1.) This is more for long-term cases, where the water loss is so severe that it is better to lose their leaves entirely

2.) It is usually a drought or seasonal-specific response

Why do we lose leaves during the winter?

Because it is so cold and there is no water available for the plant, therefore the plant purposely loses the leaves, to prevent any further damage

Alternative photosynthetic pathways

Some plant species have alternative photosynthetic pathways that helps reduce water loss, such as

1.) C4 photosynthesis

2.) CAM photosynthesis

C4 photosynthesis

1.) It occurs in 3% of plants

2.) It is usually seen in warm climates, such as the tropics or subtropics

3.) Commonly seen in grasses, corn, sugar cane, etc

CAM photosynthesis

1.) It occurs in 7% of plants

2.) It is usually seen in hot + dry environments

3.) Commonly seen in cacti, pineapples, and other epiphytes (i.e. plants that live on top of plants)

CAM and C4 photosynthesis

It adds an extra step, such that it converts CO2 into an organic acid, before it enters the Calvin cycle (i.e. dark reactions)

Reduction of water loss in C4 and CAM photosynthesis

It reduces water loss, per unit of CO2 gained

Photosynthesis in C3 plants

Both stages of photosynthesis, i.e. the light and dark reactions, occurs in the mesophyll cells

Light reactions

It captures the light energy and then funnels it into high energy carriers, creating O2 in the process

Dark reactions

It converts CO2 into sugars, using the energy provided from the high energy carriers produced from the light reactions

Role of Rubisco

The enzyme that is responsible for carrying out the calvin cycle, i.e. turning CO2 into simple sugars

Major limitation of C3 plants

1.) When O2 concentrations are high and CO2 concentrations are low, rubisco can accidentally bind O2, thereby causing photorespiration

2.) This causes a complete loss of all the captured light energy, with no sugars being made

When does photorespiration occur

It occurs when the stomata are closed, resulting in low CO2 and high O2

C4 plants

They have a different leaf anatomy, with spatial specialization that separates light and dark reactions, such that they are carried out in different cells

Light reactions in C4 plants

1.) It occurs in the mesophyll cells

2.) It fixes CO2 into an organic acid, preventing any O2 binding that may occur

3.) The organic acid is then shipped of into the bundle sheath cells

Dark reactions in C4 plants

1.) It occurs in bundle sheath cells

2.) Once the organic acid is inside the bundle sheath cell, it is broken down into CO2 once again, concentrating the amount of CO2 present for rubisco to use

3.) No light reactions occur in the sheath cells, reducing the chance of any O2 binding

Significance of concentrating CO2 in the sheath cells

It leads to a higher rate of activity for the enzyme

Why are C4 plants not the norm?

1.) It leads to very fast growth rates, but it requires high temps and high levels of light

2.) This is why C4 plants are not generally seen in Manitoba

Bundle sheath cells location

It makes up the tissue surrounding the vascular tissue, depositing the sugars made right into the vascular tissue

Vascular tissue in plants

It transports water and sugars to the rest of the plant

CAM plants

They have temporal specialization, rather than spatial specialization, such that certain processes occurs at a specific time

CAM plants at night

At night the stomata is open, allowing CO2 to come in and build a pool of organic acids

CAM plants during the day

The stomata are closed and the pool of organic acids are made into CO2 once again, to be used for photosynthesis

CAM plants advantage

Water loss is minimized by keeping the stomata closed, thereby improving water-use efficiency

Why are CAM plants not the norm?

CAM plants are slow and inefficient, because the stored carbon depletes quickly, as you can only store so much CO2/organic acid

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 do 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

Animal thermal balance

It is similar to plants, but animals differ such that they generate higher quantities of heat and they can physically escape hot and cold conditions

How do animals generate such large amounts of heat?

Through cellular respiration

Regulating the body core

It is much more important to regulate the body core than the extremities, but the body structure can be used to influence heat exchange

Using body structure to regulate the body core

1.) Muscles and fat for insulation

2.) Hair, scales, and feathers can be used to create a boundary layer

Boundary layer in humans

We have goosebumps that acts as a boundary layer, but we create a boundary layer ourselves using clothing

Temperature range of poikilotherms vs. homeotherms

Homeotherms tend to have a narrower range, while poikilotherms tend to have a wider range, but both have their lethal limits

Poikilotherms gaining heat

They primarily gain heat from the environment, therefore the environment controls the metabolism and activity of the organism

Upper and lower temperature limits of poikilotherms

They do exist, but it is relatively broad

Poikilotherms controlling their temperature

1.) They control their temperature using their behaviour, depending on what they need

2.) I.e. they will either sit in the sun or hide in the shade

Metabolic rates of poikilotherms

1.) They have low metabolic rates and therefore low rates of cellular respiration

2.) They limit themselves to short bursts of activity, as much as possible

Poikilotherms energy use

Despite the fact that they don’t have a lot of energy, due to low cellular respiration and metabolic rates, they are very efficient users of energy because they only use it when they need to

Poikilotherms sitting in the sun vs. hiding in the shade

1.) They sit in the sun when they want to increase their activity level, in order to build up energy

2.) They hide in the shade when they want to lower cellular respiration, in order to conserve energy, because they no longer need the energy