UNIT 5: Energy transfers in and between organisms (copy)

Describe the first step of the light-dependent reaction.

In the first step of the light-dependent reaction, chlorophyll absorbs light energy, leading to the photoionisation of chlorophyll.
The light energy excites electrons in chlorophyll.
The high-energy electrons are released from the chlorophyll and move down the electron transfer chain.

space for everything else x

Fill in the blanks:
In any ecosystem, plants synthesise organic compounds from ______ or ______ carbon dioxide.

In any ecosystem, plants synthesise organic compounds from atmospheric or aquatic carbon dioxide.

Fill in the blanks:
Most of the sugars synthesised by plants are used by the plant as _______ _______.

The rest are used to make other groups of ______ _______.
These biological molecules form the _____ of the plants.

Most of the sugars synthesised by plants are used by the plant as respiratory substrates.
The rest are used to make other groups of biological molecules.
These biological molecules form the biomass of the plants.

Give two ways biomass can be measured.

Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area.

What can calorimetry be used to estimate?

Calorimetry can be used to estimate the chemical energy store in dry biomass.

What is gross primary production (GPP)?

Gross primary production (GPP) is the chemical energy store in plant biomass, in a given area or volume.

What is net primary production (NPP)?

Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account.

Give the equation for net primary production.

The equation for net primary production is
NPP = GPP – R
where GPP represents gross production and R represents respiratory losses to the environment.

Give three things the net primary production is available for.

The net primary production is available for plant growth, plant reproduction, and other trophic levels in the ecosystem, such as herbivores and decomposers.

Give the equation for the net production of consumers.

The equation for the net production of consumers is N = I – (F+R)
where I represents the chemical energy store in ingested food
F represents the chemical energy lost to the environment in faeces and urine
R represents the respiratory losses to the environment.

What is primary productivity?

Primary productivity is the rate of primary production.

What is secondary productivity?

Secondary productivity is the rate of secondary production.

What are primary and secondary productivity measured as?

Primary and secondary productivity is measured as biomass in a given area in a given time
eg kJ ha^-1 year^-1.

Give two ways the efficiency of energy transfer is increased.

One way the efficiency of energy transfer is increased by simplifying food webs to reduce energy losses to non-human food chains.
Another way is by reducing respiratory losses within a human food chain.

What is recycled within natural ecosystems?

Nutrients are recycled within natural ecosystems.

Give two examples of nutrient cycles.

Two examples of nutrient cycles are the nitrogen cycle and the phosphorus cycle.

Fill in the blank:
____________ play a vital role in recycling chemical elements such as phosphorus and nitrogen.

Microorganisms play a vital role in recycling chemical elements such as phosphorus and nitrogen.

Describe the role of saprobionts in decomposition.

In decomposition, saprobionts carry out saprobiotic nutrition.
They secrete enzymes to digest food externally.
Here, organic molecules are broken down into inorganic ions by extracellular digestion.
These nutrients are then absorbed.

Define the term mycorrhizae.

Mycorrhizae are symbiotic relationships between fungi and the roots of plants.

Describe the structure of the fungi involved in the mycorrhizae.

The fungi involved in the mycorrhizae have long, thin strands called hyphae which connect to the roots of the plant.

Explain why mycorrhizae facilitate the uptake of water and inorganic ions by plants.

Mycorrhizae facilitate the uptake of water and inorganic ions by plants because the hyphae on the fungi increase the surface area of the plant’s root system.
In turn, the fungi obtain organic compounds such as glucose from the plant.

Name the five processes involved in the nitrogen cycle.

The five processes involved in the nitrogen cycle are nitrogen fixation, saprobiotic nutrition, ammonification, nitrification, and denitrification.

Describe the process of nitrogen fixation.

In the process of nitrogen fixation, nitrogen gas in the atmosphere is converted to ammonia by nitrogen-fixing bacteria.
The ammonia forms ammonium ions in solution.

Where are nitrogen-fixing bacteria found?

Nitrogen-fixing bacteria are found inside the root nodules of leguminous plants.

Describe how nitrogen-fixing bacteria form a mutualistic relationship with plants.

Nitrogen-fixing bacteria form a mutualistic relationship with plants since the bacteria provide the plant with nitrogen-containing compounds and the plant provides carbohydrates.

Describe the process of ammonification.

In the process of ammonification, DNA, RNA, and proteins from dead organisms or urea are converted to ammonia by saprobtioic nutrition.
The ammonia then forms ammonium ions.

Describe the process of nitrification.

In the process of nitrification, ammonium ions in the soil are converted to nitrites, which are then converted to nitrates.
This is done by nitrifying bacteria.

Describe the process of denitrification.

In the process of denitrification, nitrates in the soil are converted to nitrogen gas by denitrifying bacteria, during respiration.
This occurs under anaerobic conditions.

Describe two other ways nitrogen is cycled in an ecosystem.

One other way nitrogen is cycled in an ecosystem is by lightning, which fixes nitrogen gas.
Another way is by artificial fertilisers.

Describe how phosphate ions in rocks are released into the soil or bodies of water.
What happens to these ions?

Phosphate ions in rocks are released into the soil or bodies of water by weathering.
These phosphate ions are assimilated by plants or aquatic producers.

Describe how phosphate ions are transferred through the food chain.

Phosphate ions are transferred through the food chain by feeding.

Describe how phosphate ions are released BACK into the soil.

Phosphate ions are released back into the soil by saprobionts, which digest organic compounds in animal waste and dead plants and animals.

What is guano?

Guano is waste produced by sea birds.
It contains a high proportion of phosphate ions and returns a significant amount of these ions to soils in coastal areas.

Give two ways nitrates and phosphates are lost.

Nitrates and phosphates are lost by harvesting plants and removing livestock.

What is used to replace nitrates and phosphates in the soil?

Natural and artificial fertilisers are used to replace nitrates and phosphates in the soil.

Describe the difference between natural and artificial fertilisers.

Natural fertilisers are organic matter whereas artificial fertilisers are inorganic.

Give two environmental issues that arise from the use of fertilisers.

Two environmental issues that arise from the use of fertilisers are leaching and eutrophication.

What is leaching?

Leaching is when water-soluble compounds in the soil are washed away into nearby ponds or rivers by the rain or irrigation systems.

A fertiliser is applied just before heavy rainfall.
Suggest how this can affect the likelihood of leaching.

Applying a fertiliser just before heavy rainfall can make leaching more likely to occur.

Explain why leaching is less likely to occur with natural fertilisers, compared to artificial fertilisers.

Leaching is less likely to occur with natural fertilisers compared to artificial fertilisers because the nitrogen and phosphorus are still contained in organic molecules.
They must be decomposed by saprobionts before they can be absorbed by plants, controlling the rate of uptake and preventing them from being washed away.

Phosphate ions are less soluble than nitrate ions.
Suggest how this can affect the likelihood of the leaching of phosphates.

As phosphate ions are less soluble than nitrate ions, the leaching of phosphates is less likely.

Explain what causes eutrophication.

Mineral ions leached from fertilised fields cause eutrophication.
They stimulate the rapid growth of algae in ponds and rivers, known as algal blooms.

Describe the effects of algal blooms.

Algal blooms result in large amounts of algae, which block light from reaching the plants below.
The plants are unable to photosynthesise enough and eventually die.

Describe the effects of dead plants in ponds and lakes.

Dead plants in ponds and lakes are decomposed by saprobionts.
The saprobionts carry out lots of aerobic respiration, lowering the oxygen concentration in the water. This lack of oxygen causes fish and other aquatic animals to die.