B6f: Microscopic life in water Flashcards Preview

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Flashcards in B6f: Microscopic life in water Deck (15):

Explain the advantages of life in water (4)

no problem of water shortage and dehydration

less variation in temperature; aquatic organisms need not cope w/ rapid temp changes

water provides support to organisms w/o skeletal systems

easy disposal of waste products; washed away, easily dispersed, does not accumulate, greatly diluted in water and broken down


Explain the disadvantages of life in water (2)

regulating water content - water content of the body can vary and needs to be controlled

resistance to movement; water denser than air, harder to move through so more energy needed


Explain the problems of water balance caused by osmosis (2)

fresh water, animal cells have +solute conc, water enters by osmosis, swell/burst; not problem for plants; cell walls stop cells bursting, prevent excess water getting in; animals must remove excess water from body

salt­-water, animal cells have lower ­solute concentration, water leaves body via osmosis, shrivel and die; many invertebrates have bodies at same salt concentration so no problem


How do amoeba and other microscopic animals get rid of excess water?

microscopic animals (amoeba) have contractile vacuole; fills with excess water from osmosis, moves to cell membrane, fuses with cell membrane, and contracts to release water outside cell


Describe how light varies at different depths and in different seasons in water, and how this affects phytoplankton (2)

+day length (summer, spring), +light available for photosynthesis, +rate of photosynthesis, +energy for growth/reproduction, +phytoplankton

light only penetrates surface waters, phytoplankton limited to those waters


Describe how temperature varies at different depths and in different seasons in water, and how this affects phytoplankton (2)

+surface water temperature (spring, summer), +rate of photosynthesis, +energy for growth/reproduction, +phytoplankton

deep water temp is constant 4 degrees celcius, too cold for phytoplankton to grow, so they live near surface


Describe how minerals vary at different depths and in different seasons in water, and how this affects phytoplankton (2)

+depth, +mineral concentration, but phytoplankton limited there by light and temperature

in summer near the water's surface mineral concentration is low and limits the rate of photosynthesis


How do seasonal changes in phytoplankton numbers influence numbers of zooplankton?

spring/summer, +phytoplankton/algal bloom, +food for zooplankton, +zooplankton (vice versa for winter/autumn)


What are phytoplankton?

photosynthetic microorganisms; producers in aquatic food chains and webs


What are zooplankton?

animal­like microorganisms; consumers in aquatic food chains and webs


Grazing food webs (2)

begin w/ photosynthetic producers

most common in the surface layers of the oceans because more light for photosynthesis


What do other aquatic food chains rely on? (2)

detrital food chains (deep water, no light, no photosynthesis, no phytoplankton;) rely on 'marine snow' - dead food falling from above ­ as source of nutrients

bacteria, deep in ocean, act as producers that get their energy from chemical reactions (via chemosynthesis)


Eutrophication stages (5)

1. sewage/fertiliser run­off into rivers/lakes

2. +conc of nitrates/phosphates in the water; algae use these minerals to grow rapidly, produce thick green layer above (algal bloom)

3. blocks sunlight to plants in water, die + decay

4. aerobic decay bacteria use up oxygen

5. animals in water unable to respire and die


How can biologists determine pH and oxygen levels in water?

by looking for the presence/numbers of indicator species ­ species sensitive to diff pHs and oxygen levels


Explain the effect of PCBs and DDT on animals such as whales (4)

chemicals absorbed by organisms at bottom of food chain

doesn't break down/egested so when organism eaten, they are passed on

+concentration in organisms at each trophic level up the food chain as each organism eats many organisms in lower trophic levels

in higher trophic level, whales accumulate toxic levels of chemical in body; suppresses immune system, ­-population