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Quiz Friday!. covering: the physical environment biomes physiological ecology (today and Wednesday). Physiological Ecology. Two themes : Homeostasis – maintenance of constant internal conditions in varying environments Adaptation of organisms to specific environments. Three big problems.

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Quiz Friday!

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Quiz Friday!


  • the physical environment

  • biomes

  • physiological ecology (today and Wednesday)

Physiological Ecology

Two themes:

  • Homeostasis – maintenance of constant internal conditions in varying environments

  • Adaptation of organisms to specific environments

Three big problems

  • Obtaining energy and nutrients

  • Maintaining temperature

  • Obtaining and holding onto water


  • All organisms require energy to live and reproduce

  • Heterotrophs – acquire energy from organic material, live or dead

    • most animals feed on living organisms

    • decomposers (fungi, some animals) feed on dead organisms

Autotrophs – acquire energy from sunlight or chemicals in the environment

  • Chemosynthetic autotrophs:

    • obtain energy from inorganic chemicals like methane or hydrogen sulfide

    • sea-vent bacteria

  • Photosynthetic autotrophs:

    • combine energy from sunlight and CO2 to make sugars

    • many bacteria, some protists (algae), and nearly all plants

Chemical equation for photosynthesis:

energy + 6CO2 + 6H2O → C6H12O6 + 6O2

(sunlight) (from air) (from soil) (sugar) (to air)

Question 1. Interpret this graph

Overstory plant

Rate of photosynthesis

Understory plant

Light level

  • All organisms store and use energy in the form of carbon compounds

  • Respiration – the process of breaking up carbon compounds to release CO2 and energy

C6H12O6 + 6O2→ energy + 6CO2 + 6H2O

  • Other important nutrients (and their uses)

    • Nitrogen - proteins

    • Phosphorus – many chemicals

    • Sulfur – proteins

    • Potassium – ion in cells

    • Calcium – bone, wood, cell signalling

    • Magnesium – chlorophyll, enzymes

    • Iron – hemoglobin, enzymes

  • Lack of nutrients can limit plant growth


  • Water contains dissolved substances – solutes

  • Water moves from regions of low solute concentration to high concentration

  • Movement of water across a membrane is osmosis

High solute concentrations attract water with a force known as osmotic potential.

  • Water moves freely across cell membranes

  • Relative to the outside environment, a cell can be:

    • hypo-osmotic: having a lower solute concentration than the environment

    • hyperosmotic: having a higher solute concentration than the environment

    • iso-osmotic: having the same solute concentration as the environment

If left unchecked, osmosis will lead to equilibration of solute concentrations in and outside of cells

Hypo-osmotic Iso-osmoticHyperosmotic

Question 2. What happens to the slugs?

  • For organisms, the challenge is maintaining proper concentrations of solutes in cells (homeostasis).

    • semipermeable membranes – some molecules cannot pass

    • active transport – moving molecules across the membrane, requires energy

Transpiration – when plants lose water to the atmosphere as they obtain CO2


Plants must take up water at their roots to make up for transpiration

Plants use osmotic potential to draw water into their roots (root cells are hyperosmotic)

Water is pulled up through the xylem into the leaves.

Water leaves the plant through the stomata (transpiration).

  • Soil particles hold water at their surfaces against gravity.

  • Smaller particles hold more water.

  • Sandy soils have less water available than silts.

  • Water loss from stomata increases with temperature.

  • Adaptations to prevent water loss in dry environments:

    • hairs and spines

    • thick, waxy covering on leaves

    • stomata located deep in pits

    • shedding leaves in dry season

    • wilting or closing leaves


  • Finish up water relations

  • Temperature

  • The bigger picture

Question 1. Interpret this graph

Overstory plant

Rate of photosynthesis

Understory plant

Light level

Question 2. What happens to the slugs?

CO2 + RuBP → 2 PGA → sugar

(1 carbon) (5 carbons) (3 carbons)

  • Normal photosynthetic pathway:

  • Requires a lot of CO2, so stomata must be open, allowing water loss

  • Water loss is a big problem in dry places

C4 Photosynthesis – spatial separation

  • Mesophyll cell, near leaf surface:

  • Bundle sheath cell, in leaf interior:

  • Occurs in many plants found in hot, dry places (corn)

CO2 + PEP → OAA (reaction requires little CO2)

(1 carbon) (3 carbons) (4 carbons)

OAA → PEP + CO2 → photosynthetic pathway

(4 carbons) (3 carbons) (1 carbon)

  • CAM Photosynthesis – temporal separation (Crassulacean Acid Metabolism)

  • Nighttime reaction (stomata open):

  • Daytime reaction (stomata closed):

  • Occurs in succulent plants, cacti


(1 carbon) (3 carbons) (4 carbons)


(4 carbons) (3 carbons) (1 carbon)

Water Acquisition in Animals

  • Wet environments

    • drinking

    • absorbing from the environment (amphibians)

  • Dry environments

    • metabolic water (C6H12O6 + 6O2→ 6CO2 + 6H2O)

    • water in food sources (insectivores)

    • water reabsorbed in digestive/excretory systems

Water Balance in Marine Animals

  • Marine invertebrates maintain iso-osmotic internal solute concentrations equal to seawater

  • Marine fish are hypo-osmotic compared to seawater.

    • they gain solutes and lose water

    • solutions:

      • constant drinking

      • secreting salt into the water

  • Sharks and rays have high concentrations of solutes in their blood, making them iso-osmotic compared to seawater.

    • To maintain proper concentrations of ions, sharks keep urea in the bloodstream.

  • Water Balance in Freshwater Fish

  • Freshwater fish are hypo-osmotic compared to water and absorb water continuously.

  • They excrete large quantities of diffuse urine while actively retaining salts.

Organisms in variable environments adjust their solute levels based on the salinity of the water.


Why does temperature matter?

  • At hot temperatures

    • biological processes speed up

    • proteins and other organic compounds may break down

  • At cold temperatures

    • ice crystals may damage or destroy cells

    • life processes slow or stop

  • Homeothermic organisms maintain constant body temperature (birds and mammals)

  • Poikilothermic organisms have varying body temperature, in response to external temperatures (all other animals)

  • BUT poikilothermic animals may regulate their body temperature…

  • Endothermy – body heat generated internally

  • Ectothermy – body heat generated externally

  • Most ectotherms regulate their body temperature by

    • basking

    • moving between shade/sun

    • being active at certain times of day

  • Endothermy requires a lot of energy

  • Alternative is torpor – condition of lowered body temperature and activity

  • Countercurrent Circulation

  • Reduce rate of heat loss to the environment by creating a temperature gradient.

  • Heat is transported from arterial blood leaving the body to venous blood returning to the body.

Optimum – narrow range of environmental conditions to which an organism is best suited

Each organism has an optimum environment…

Local optimum:

  • Distributions of plant species are determined by precipitation and temperature

  • Ecological tolerance is the range of conditions within which a species can survive

  • Sugar maple:

  • summer temps: below 24ºC

  • winter temps: above -18ºC

  • annual precip.: > 50 cm

Different species have different ecological tolerances.

  • Species vary in how wide their ecological tolerance is

    • specialists have a narrow range of tolerance

    • generalists have a wide range of tolerance

Quiz Friday!


  • the physical environment

  • biomes

  • physiological ecology (slides on the website later today)

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