Biology: Photosynthesis Pathways (C3, C4 & CAM)

Exam Format

• Scheduled for Wednesday, March 12.
• The location is Bolton B60.
• A pen or pencil will be required.
• It consists of 8 short answer questions.
• You need to answer 6 questions compulsorily.
• If you decide to answer all 8:
• The best 6 answers will be graded and count towards the exam grade.
• The remaining 2 can be used for extra credit.

Photosynthesis

• Photosynthesis is the sole process capable of converting CO₂ into organic molecules, and only plants can perform it.
• All animal life on Earth is carbon based.
• Photosynthesis forms the basis of all food chains.
• Stomata must remain open so CO₂ can be taken in but this results in water being lost.

3 Photosynthetic Pathways

• C3, C4, and CAM pathways

C3 Pathway

• Ideal for cool, humid conditions.
• Some CO₂ is converted into a 3-carbon molecule.
• Not very efficient because some CO₂ reacts with O₂, wasting carbon along the way.

C4 Pathway

• Adapted for hot, dry environments.
• Converts most CO₂ into a 4-carbon molecule.
• More efficient than C3, plus stomata doesn't need to stay open as long to operate.

CAM Pathway

• Best for hot, very dry conditions.
• CO₂ is absorbed at night and stored as a 4-carbon molecule.
• The C3 pathway is used during the day.
• C4 plants generally have the highest rate of photosynthesis, while CAM plants have the lowest.

Plant Examples for Each Pathway

• C3 includes wheat, rice, soybeans, legumes, and many trees; typically found in cool, moist climates.
• C4 includes maize, sorghum, sugarcane, and prairie grasses; adapted to hot climates due to efficient CO₂ uptake.
• CAM includes sisal, pineapple, cactus, plants combine C3 and C4 photosynthesis, found in hot, very dry climates, and store CO₂ at night to conduct photosynthesis during the day.

Hierarchies

• Hierarchies are used to categorize and organize constituents.
• A hierarchy is a system where components are ordered by rank.
• Biogeography contains three important hierarchies: taxonomic, ecological, and trophic.

Trophic Hierarchy

• Also known as a food chain or food web.
• Autotrophs, like plants and algae, are primary producers.
• Primary producers are eaten by primary consumers (caterpillar).
• Primary consumers are eaten by secondary consumers (passerine).
• Secondary consumers are eaten by tertiary consumers (passerine).
• Apex predators are at the very top of the food chain (raptor).
• Heterotrophs are consumers like herbivores and carnivores that cannot make their own food.
• Decomposers consume both plant and animal matter.

Animals

• Animals experience temperatures ranging from Antarctic to hot desert.
• Most animals require 0-40°C to survive.

Strategies for Managing Temperature

• Ectotherms obtain heat from the environment, such as invertebrates, fish, amphibians, and reptiles, through sunning.
• Endotherms produce heat metabolically from food breakdown, including birds and mammals.
• Homeotherms maintain a relatively constant body temperature.
• Poikilotherms see body temperature fluctuate significantly and regularly.

Bergmann's Rule

• Endothermic vertebrates in colder environments tend to have larger body sizes.
• Larger body sizes have a lower surface area to volume ratio which allows them to maintain heat much more readily.

Allen's Rule

• Endothermic vertebrates have shorter, more compact limbs in colder environments so they can maintain heat.
• Shorter, compact limbs have a lower surface area to lose heat from.

Thermoregulation

• Homeotherms are able to exploit a wider range of thermal environments and therefore need larger amounts of energy to control thermal regulation.

Ways to Stay Warm

• Insulation using fur, feathers, and fat.
• Shivering, which is involuntary muscular activity.
• Huddling together to share body heat.

Ways to Stay Cool

• Evaporation of moisture from skin in birds and mammals.
• Sweating which removes heat as water evaporates, e.g. horses and humans.
• Gular fluttering where birds flap membranes in their throat.
• Kangaroos produce saliva and lick themselves to cool down.
• Avoidance by burrowing or being less active during the hottest parts of the day like cheetahs.

Moving and Avoiding

• To avoid temperature extremes.
• Birds and insects can fly to avoid temperature extremes by migrating.
• Fish can swim to different depths to avoid temperature extremes.
• Reptiles and mammals can walk.
• Burrowing to avoid temperature extremes.
• Hibernating to avoid temperature extremes.
• Camoflage or Pigmentation helps chameleons become darker in cooler temperatures.
• Large ears like the African elephant.
• Large body size, blubber, water repellent fur like the polar bear.

Biological Interactions

• No organism exists in isolation.
• Types include predator and prey, plant and pollinator, and pathogen and host.
• Competition for resources.
• Symbiosis through relationships between organisms.
• Interdependence in phenology which is nature's calendar.

Population Regulation

• The environment limits population growth by altering birth and death rates, which relies on density dependence.

Density-Dependent Factors

• Disease and resource competition affect populations in proportion to their size, slowing the rate of increase.

Density-Independent Factors

• Natural disasters and human activities like deforestation influence populations regardless of the number of individuals.

Intraspecific Competition

• Density-dependent.
• Increases gradually, affecting growth and development, then individual survival and reproduction.

Ecosystem Disturbances

• Disturbances are short in duration and destructive.
• Vital for long-term functioning of ecosystems.
• Disturbances cause succession.
• Types of disturbance is fire, flooding, wind, pathogen/pests, humans, etc.

Succession

• A retreat of glaciers reveal bare rock that is deprived of organic matter but rich in other elements.
• Sitka alder (Alnus sinuata) fertilizes the soil through a process called N fixing which then allows other plants to thrive.
• Sitka spruce (Pices sitchensis) assumes dominance after 80 years through a process called facilitation-progressive development.

Animal Species Diversity

• It increases after a disturbance, in an ecosystem, which leads to Open Canopy, Grasses, Low to High Shrub, Pole Shrub to Pole Timber, and Closed Canopy.

Reconstructing Past Climate

• A climate proxy is an indirect source of evidence used to reconstruct past climate conditions.
• Proxies include air trapped in ice sheets & glaciers, marine sediments, biological proxies, dating techniques, peatbogs/lakes, pollen analysis, radio-carbon dating, speleothems, clams, tree rings, and historical records.
• All reflect historical temperature, precipitation, and atmospheric composition.

Geological Time

• Geological time scale determines the age of the Earth.
• According to Archbishop James Ussher of Armagh and Primate of all Ireland 1625-1656, it happened on Sunday, October 23, 4004 BC at 6pm, the night preceding.
• John Joly, 1898, estimated the Earth to be 80-100 million years old based on the accumulation of sodium in the ocean.

Plate Boundaries

• Divergent boundaries sees new lithosphere forms as plates pull apart which is seen in Iceland.
• Transform boundaries sees plates grind past each other creating no change in Lithosphere which is seen in San Andreas.
• Convergent boundaries sees one plate dive beneath another which is called subduction. When this occurs, two plates collide which is called ocean-ocean/ land-land/ocean-land.

Hot Spots

• Hawaiian Islands arise in the middle of the Pacific Plate where magma rises up on the sea floor.

Convergent Boundaries (Ocean to Ocean)

• Two oceanic crust plates collide.
• Denser plate usually subducts, site of Island Arc formation.

Divergent Boundaries

• They lead to island formation, e.g. Iceland & Azores.
• Undersea mountain range or intense volcanic activity.

Evolution

• Descent with modification.
• Small-scale evolution is changes in gene frequency in a population from one generation to the next.
• Large-scale evolution is descent of different species from a common ancestor over many generations involving populations, not just individuals.
• Biological evolution not just change over time.

Descent with Genetic Inheritance

• Includes trees losing leaves, mountains erode.
• Includes a common ancestor.

History of Life

• Different species share common ancestors.
• Illustrated by family tree or phylogeny.

Extinction

• Occurs when the last individual of a species dies out.
• Local extinction occurs like what happened to the American Buffalo (bison).
• Global extinction occurs when a species is lost over its entire range.
• Dna techniques may allow cloning a mammoth.
• Occurs when the environment of a species changes faster than the species can adapt.
• Nearly all of the species that have existed on Earth have gone extinct.
• There have been 5 major mass extinctions in geological history.
• Recovering from these extinctions can take millions of years

Mass Extinctions

• Sudden decrease in number of species in a short period of time.

Background Extinction

• Plant families going extinct 1 every 4 million years.
• Decline is a sharp drop in speciation (loss of genes) which sees Rate of extinction increasing compared to speciation
• At least 5 instances have occurred in Earth's history of Mass Extinctions.
• The last one was 65 million years ago.
• Marine fossils most widely used to measure extinction rates
• Characterized by rapid decline.

After the Meteorite Strike at Chicxulub

• Heat and shock waves would have killed everything within several thousand km.
• A Huge tsunami would have inundate coastal areas causing more deaths.
• Dust from impact and resulting fires would have darkened atmosphere & cause global T to plummet, lethal to many plants and animals.
• Precipitation would have been acidic due to sulphur and nitric acid formation due to heating of the atmosphere.
• Once dust settled high amounts of CO2 and water vapour in the atmosphere would cause extreme greenhouse warming.

Theories for Dinosaur Decline

• Climate change caused seasonality caused fragmentation of feeding grounds.
• Hatchling failure due to selenium intake.
• Skewed sex ratio due to change in temperature.

After the Dinosaurs

• Radiation of mammals.
• Also flowering plants, insects, and birds.
• Radiation of flowering plants and insects at the same time due to coevolution.