mod 2.2 - nutrient and gas requirements Flashcards
What are autotrophs?
Autotrophs, or producers make their own energy by converting inorganic compounds (eg: carbon dioxide and water) to organic compounds.
The process of converting inorganic carbon into organic compounds is called carbon fixation, because the autotroph ‘fixes’ the inorganic carbon into organic molecules such as glucose.
These organic compounds are then consumed by heterotrophs.
What further groups are autotrophs divided into according to how they obtain the energy required for carbon fixation?
Photosynthetic autotrophs/photoautotrophs: which use light energy.
Chemosynthetic autotrophs/chemoautotrophs: which use chemical energy.
What are photosynthetic autotrophs?
They obtain energy required for carbon fixation from light or solar energy.
They undergo photosynthesis, and produce the organic compound glucose (in plants).
Most autotrophs are photosynthetic; all green plants but also algae, Euglena and cyanobacteria.
Explain the photosynthetic autotroph Venus flytrap.
Carnivorous plants, such as the Venus flytrap (Dionaea muscipula) obtain some nutrients such as nitrogen, potassium and phosphorus by capturing and consuming other organisms. However, because they obtain most of their organic compounds through photosynthesis, they are considered as photosynthetic autotrophs.
What are chemosynthetic autotrophs?
Obtain energy required for carbon fixation from inorganic chemical reactions (chemosynthesis). All known chemosynthetic organisms are prokaryotes. Come chemoautotrophs obtain energy by the oxidation of inorganic molecules. eg: Ammonium ions (NH4+) to nitrite ions (NO2-) Nitrite ions (NO2-) to nitrate (NO3-) Sulfide ions (S2-) to sulfide ions (SO42-) Chemoautotrophs can live in the more extreme environments where these ions can be found → extremophiles.
What are examples of chemoautotrophs?
Methanogens live in places with low oxygen (digestive tracts of animals and in wetlands) where they obtain energy from a carbon-fixing reaction in which carbon and hydrogen react to form a simple organic compound: methane.
Archaea that live off the carbon in coal.
Bacteria that convert sulfur to sulfate in deep sea thermal vents.
Various nitrifying bacteria that fix nitrogen gas from the air or convert ammonia to nitrate to nitrate ions underground, helping plant growth in the process.
Denitrifying bacteria that return nitrogen to the air.
Bacteria that decompose crude oil.
What are heterotrophs?
They obtain organic compounds by consuming other organisms or their products.
Heterotrophs use the nutrients organic compounds contain they consume to obtain energy.
All heterotrophs depend directly or indirectly on autotrophs for nutrients and energy.
All animals and fungi are heterotrophs; and some bacteria and many protists.
What are photoheterotrophs?
These are specialised prokaryotes that use solar energy, rather than organic compounds as a source of energy.
However, unlike photoautotrophs, photoheterotrophs cannot fix carbon from carbon dioxide into organic compounds; so they use organic compounds obtained from other organisms as their carbon source for growth and renewal, not as an energy source.
eg: green non-sulfur bacteria, purple non-sulfur bacteria and heliobacteria.
What are chemoheterotrophs?
Most heterotrophs are chemoheterotrophs.
They obtain energy from organic compounds by cellular respiration.
Animals, protists, fungi and most heterotrophic bacteria are chemoheterotrophs.
These can further be divided into groups:
What are herbivorous heterotrophs?
Animals that only eat plant material (herbivores).
eg: kangaroos, horses, parrots, caterpillars and snails.
What are carnivorous heterotrophs?
Animals that only eat other animals (carnivores).
eg: dingoes, eagles, crocodiles, sharks and spiders.
What are omnivorous heterotrophs?
Broad dieted animals that eat a mixture of both plants and animals.
Omnivores are opportunistic eaters, eating foods that are readily available to them.
eg: humans, bears and lizards.
What are saprotrophic heterotrophs?
Include most fungi and some bacteria.
They eat by digesting organic material by extracellular means; meaning they secrete enzymes onto dead and decaying organic material, such as carcasses, leaf litter or fruit. Once the enzymes have broken down the large molecules, the saprotrophic organisms absorb the simple organic nutrients through endocytosis.
This process of decomposing and recycling organic matter is essential for ecosystems to function, as the process returns nutrients back into the environment, driving the cycle of energy.
What are parasitic heterotrophs?
Also known as parasites, derive their energy and nutrients directly from other living organisms.
They feed on the cell contents, tissues or body fluids of their host.
Their host is harmed and sometimes killed in this process.
Parasites are highly diverse and can be found in all five kingdoms.
What are endoparasites?
Parasites that live in the host. (eg: tapeworms, liver flukes)
What are ectoparasites?
Parasites that live outside the host. (eg: ticks and lice)
What is the carbon source of autotrophs?
Carbon dioxide.
What is the carbon source of heterotrophs?
Organic compounds.
What is the energy source of photoautotrophs?
Solar energy (sunlight).
What is the energy source of chemoautotrophs?
Inorganic molecules.
What is the energy source of photoheterotrophs?
Solar energy (sunlight).
What is the energy source of chemoheterotrophs?
Organic compounds.
Where does gas exchange in plants occur?
Occurs through the stoma (plural stomata). Plants conduct gas exchange through their stomatal pores in their leaves.
Where is the stomata located?
It is the opening to an air space located in the lower epidermis on a leaf, and consists of two highly epidermal cells: guard cells. These guard cells surround a pore, creating an opening through the epidermis and cuticle.
What is the stomata’s function?
Stomata are open during the day to increase the rate of photosynthesis when sunlight is available.
When the guard cells are turgid, or swollen, the stomatal opening is large, allowing water and gases to enter and exit the leaf. They become turgid when potassium ions (K+) accumulate and the water potential of the guard cells decreases.
The stomata close when light levels drop and the plants don’t need any more carbon dioxide gas for photosynthesis.
When guard cells lose water, the cells become flaccid and the stomatal opening closes, preventing water and gas from leaving the plant.
How do stomata regulate gas exchange?
When plants open their stomata to allow carbon dioxide gas in for photosynthesis, oxygen gas is released, and water is lost as water vapour during the process of transpiration (the passive movement of water through a plant from the roots and its evaporation as water vapour through the stomatal pores in leaves). Transpiration involves the upwards movement of water against the force of gravity (transpiration-cohesion-tension theory → see module 2.3).
What happens when the stomata is open?
When the stoma is open (depending on temperature), water is lost which is important as it draws water in from the soil.
When water availability is decreased, photosynthesis is limited and carbon dioxide increases as cellular respiration occurs.
Only on really humid days do stomata stay open as water concentration is equal.
What are the gas exchange structures in plants?
Stomata, lenticels and chloroplasts.
What are lenticels?
Pores on the woody parts of plant and shrubs,
Diffusion of water, carbon dioxide and oxygen occur here, but this is slow as woody parts of plants don’t require oxygen.
What are chloroplasts?
Photosynthesis occurs here.
Each chloroplast has an outer and inner membrane which regulate the movement of materials into and out of the organelle.
Inside these membranes is a fluid matrix called stroma and a highly complex inner thylakoid membrane system, which fold to form flat hollow discs, which form stacks called grana (singular: granum). Between the grana are flat membrane sheets called thylakoid lamellae (singular: lamella).
How does carbon dioxide affect photosynthesis?
If the stomata are closed, photosynthesis will use up the carbon dioxide available, reducing the carbon dioxide concentration in the leaves.
With less carbon dioxide available, the rate of photosynthesis will be limited, even with the presence of light.
How does water affect photosynthesis?
The amount of water used in photosynthesis is small compared with the amount needed to keep the cells alive, therefore a living plant cell will normally have sufficient water for photosynthesis to occur.
When the water availability is low and a plant is suffering from water stress, the stomata in the leaf close to conserve water → which limits the amount of carbon dioxide that can enter the leaves for photosynthesis.
How does light energy affect photosynthesis?
The limit will be the point at which all the photosynthesis systems and enzymes in the chloroplasts are working at their optimum rate.
In the natural environment, the amount of light available for photosynthesis depends on the amount of sunlight.
Trees and taller plants shade plants on the forest floor, while the amount of light available to aquatic plants depends on how fair underwater they will grow.
Sunlight will also vary during the cycle of a day and will change with the seasons and the weather.
What are vascular plants?
They usually grow in terrestrial environments, and are characterised by the presence of vascular tissue, which is specialised for transporting fluids.
Vascular tissue includes:
Xylem: transports water and inorganic nutrients (mineral ions) absorbed from the soil up the plant.
Phloem: transports dissolved sugars produced by photosynthesis from the leaves throughout the plant, and organic substances such as amino acids.
What is the root system of plants?
The root tissue of plants is usually located in the soil and is not visible without extracting a plant from its soil bed.
Roots have a critical role in anchoring a plant to the soil, as well as absorbing water and dissolved minerals from the soil for growth and photosynthesis.
Roots also store glucose produced by the plant.
How is water transported into roots?
Water travels into root hairs through osmosis. Dissolved ions (minerals) from the soil come into root hairs by diffusion. Roots require air; they go through aerobic respiration.
What are the layers of roots?
Roots have structural adaptations that help them absorb water → the exterior of the root is the epidermis, composed of epidermal cells. Some of these epidermal cells have long, fine extensions called root hairs, which increase SA and maximise water and mineral uptake.
The next layer of a root is the cortex, which is composed of parenchyma cells, which can store nutrients and starch.
The innermost central region of the root contains the vascular tissue: xylem and phloem.
What is the shoot system?
This system is above the soil, and offers support and allows for the transport system inside the shoot system.
Dermal tissue (outside of the shoot system) offers support and is waterproof.
Guard tissue: tissue that fills out the stem.
What are the layers of leaves?
In vascular plants, a leaf is an organ composed of three distinct layers of specialised cells, or tissues: upper epidermis, mesophyll and lower epidermis.
What is the structure and function of the cuticle?
Thin, waxy waterproof layer. It protects the inner cells, prevents water loss and allows sunlight to penetrate for photosynthesis.
What is the structure and function of the epidermis (upper and lower)?
Transparent and usually thin. Protects the inner cells, prevents water loss and allows sunlight to penetrate for photosynthesis.
What is the structure and function of the epidermis and cuticle?
Contains guard cells surrounding guard cells surrounding stomata. Regulates gas exchange and water loss– the waxy cuticle protects the lead from excess water loss and the opening and closing of the stomata controls the amount of gas and water vapour entering and exiting the leaf.
