importance final exam

What is abiotic stress and what are its main impacts on plants?

• Caused by non-living environmental factors outside the normal range.

• Includes drought, flooding, heat, salinity, ozone and elevated CO2.

• Reduces plant growth, photosynthesis, physiology and yield.

• Climate change is increasing the frequency and severity of abiotic stress.

What are the main functions of roots, stems, xylem and phloem?

• Roots absorb water and nutrients, store carbohydrates and anchor the plant.

• Root hairs increase surface area for water uptake.

• Stems support the plant and transport materials.

• Xylem transports water and dissolved minerals from roots to leaves.

• Phloem transports sugars from source tissues to sink tissues.

How does water move through plants?

• Water enters roots by osmosis.

• Transpiration creates negative pressure in the xylem.

• Cohesion-tension theory explains how water molecules stay together through hydrogen bonding.

• Adhesion helps water stick to xylem walls.

• Root pressure becomes more important when transpiration is low.

What is the role of stomata in plants?

• Stomata regulate gas exchange.

• CO2 enters for photosynthesis.

• Water vapour leaves through transpiration.

• Guard cells control opening and closing using turgor pressure.

• Under drought or heat stress, stomata close to reduce water loss.

• Closed stomata also reduce CO2 uptake and photosynthesis.

What are the main stages of photosynthesis?

• Photosynthesis includes light-dependent and light-independent reactions.

• LD: produce ATP + NADPH

• LI: uses ATP and NADPH to make glucose from CO2.

• Rubisco is the main enzyme in the carbon fixation.

• Photorespiration occurs when Rubisco reacts with oxygen instead of CO2.

How does heat stress affects plants?

• High temperatures reduce crop yields.

• Heat stress increases respiration and reduces biomass.

• Heat damages enzymes, membranes and photosynthesis.

• Extreme heat reduces flowering, seed set and grain filling.

• Yield losses are often worse in already warm regions.

How does waterlogging affect soils and plants?

• Water-logging reduces oxygen availability in soil.

• Low oxygen reduces root respiration and nutrient uptake.

• Causes soil compaction, toxic ion accumulation and increased bulk density.

• Reduces microbial activity and mineralisation.

• Lowers photosynthesis, stomata conductance and root hydraulic and conductivity.

• Reduces nitrogen fixation.

• Leaves yellow as chlorophyll degrades.

How does elevated CO2 affect crops?

• Elevated CO2 can increase photosynthesis, especially C3 plants.

• Often lowers protein, iron, zinc and nitrogen concentrations.

• Carbohydrate production increases faster than nutrient uptake.

• Can improve yield quantity but reduces nutritional quality.

• May worsen hidden hunger and malnutrition globally.

How does tropospheric ozone affect plants?

• Ozone damages plan tissues and reduces growth.

• Reduces photosynthesis and crop yields.

• Can reduce soil fertility.

• Often causes visible leaf injury and lower productivity.

What are the main effects of osmotic stress on plants?

• Reduced water potential

• Cellular dehydration

• Reduced metabolism

• ROS production

• cell death

• Wilting and burnt leaves

Why is drought harmful to plants?

• Reduced water uptake

• Causes stomata closure

• Lowers photosynthesis

• Reduces nutrient transport

• Reduces flowering and seed production

What are the four main plant responses to drought?

• Drought escape

• Drought avoidance

• Drought tolerance

• Drought resistance

What are the common drought adaptations?

• Deep roots

• Thick cuticle

• Rolled leaves

• CAM photosynthesis

• Root hair elongation

• Water storage tissues

What is the role of ABA in drought stress?

• Main drought stress hormone

• Causes stomata closure

• Changes guard cell volume

• Activates stress-response genes

How does waterlogging affect plants?

• Reduces oxygen in soil

• Causes hypoxic and anoxic conditions

• Damages roots

• Reduces nutrient uptake

• Lowers photosynthesis

What is the role of ethylene in flooded plants?

• Controls stress responses

• Promotes aerenchyma formation

• Helps oxygen move through roots

• Can induce cell death and cell separation

How does deep water rice survive flooding?

• Elongates internodes rapidly

• Forms hollow snorkels

• Allow gas exchange above floodwater

What are the main effects of cold stress on plants?

• Membrane damage

• Electrolyte leakage

• Slower metabolism

• Leaf curling and discolouration

• Reduced growth and vigour

What are the main effects of heat stress on plants?

• Reduced yield and fruit weight

• Lower chlorophyll and photosynthesis

• Increased oxidative stress

• Sterility and abnormal seeds

• Leaf scorch and senescence

How does temperature affect photosynthesis?

• Heat damages membranes and electron transport

• Drought closes stomata and reduces CO2 uptake

• Cold slows enzyme reactions in the Calvin cycle

• Too much light can damage photosynthesis

What are HSF and HSP?

• HSF: activate stress-response genes.

• HSP: protect plants during heat stress

• They help plants survive high temperatures

What are the main types of frost damage?

• Ice formation inside and outside cells

• Membrane damage

• Osmotic stress

• ROS production

• Xylem embolism

How does salinity affect plants?

• Causes osmotic stress

• Reduces water uptake

• Damages enzymes and photosynthesis

• Reduces growth and productivity

How do plants tolerate salinity?

• Store sodium in vacuoles

• Exclude sodium from leaves

• Use osmotic adjustment

• Halo hates have salt glands

What is the disease triangle?

• Susceptible host

• Pathogen

• Favourable environment

What causes most plant diseases?

• Bacteria and Fungi

What is Pierces disease?

• Disease of grapevines.

• Caused by Xylella fastidiosa

• Spread by sharpshooter insects

What factors increase the risk of Pierces disease?

• Warm winters

• Susceptible grape variants

• High vector populations

• Longer exposure to insects and bacteria

How can climate change increase plant disease?

• Warmer conditions favour pathogens

• Insect vector survive longer

• Longer growing seasons increase exposure

• Mild winters increase disease spread

How does global warming affect the water cycle?

• Speeds up the water cycle

• Warmer air holds more water vapour

• Changes rainfall and salinity patterns

How does temperature affect fish?

• Changes in metabolism

• Affects feeding and spawning

• Influences growth, survival and distribution

Why does ocean warming reduce dissolved oxygen?

• Oxygen is less soluble in warm water

• Warmer oceans contain less dissolved oxygen

• Can lead to hypoxia of hypercapnia

What is hypoxia?

• Low dissolved oxygen in water

• Makes survival difficult for many marine organisms

What causes ocean acidification?

• Burning fossil fuels

• Deforestation

• Oceans absorb 30% of release CO2

What is hypercapnia?

• Excess CO2 in organisms

• Causes glycogen depletion

• Increases amino acid and lipid use

How does OA affect calcification?

• Lowers pH and carbonate ions

• Reduces shell and skeleton formation

• Causes malformed structures

Why are pteropods important in OA studies?

• They shells dissolve in low pH water

• They are important prey for salmon

What is the solubility pump?

• Cold water absorbs more CO2

• Moves CO2 to deep ocean waters

What is the carbonate pump?

• Driven by marine organisms making CaCO3

• Important for storing carbon in the ocean

• What is the soft tissue pump?

Organic carbon sinks from surface waters

• Helps remove CO2 from the atmosphere

• If stopped, atmospheric CO2 could rise by 150-220 ppm

What is a species niche?

• The range of conditions where a species can survive.

• Includes abiotic and biotic factors.

What are the main abiotic and biotic factors affecting species?

• Abiotic: temperature, water and nutrients

• Biotic: prey, competition and mutualism

What is phenology?

• Timing of life history events

• Includes flowering, migration and breeding.

What causes phenological shifts?

• Changes in temperature and rainfall

• Different species respond at different rates.

What is trophic mismatch?

• When interacting species become out of sync

• Can affect pollination and predator-prey relationships

What are the three main types of mismatch?

• Temporal mismatch

• Spatial mismatch

• Morphological mismatch

How can climate change affect bees and flowers?

• Flowers may bloom earlier

• Bee timing may stay the same

• Reduced pollination lowers seed production

What is an example of spatial mismatch?

• Agave plants and bats shifting into different areas

What are the main features of arthropods?

• Exoskeleton

• Jointed appendages

• Segmented body

• Compound eyes

• Specialised respiratory system

What is the function of the arthropod exoskeleton?

• Protection

• Support

• Muscle attachment

• Reduces evaporation

Why do arthropods moult?

• They exoskeleton cannot stretch

• Growth requires shedding the old cuticle

What is the difference between expoterygotes and endopterygotes?

• Expo: wings develop outside and no pupal stage

• Endo : wings develop internally and complete metamorphosis

Why are insects important?

• Pollinate plants

• Food source for animals

• Can be pests or disease vectors

• Useful in biological control

What is eusocial behaviour?

• Cooperative living

• Division of labour

• Reproductive castes

• Overlapping generations

What is temporal polyethism?

• Changes in tasks with age

• Example: nurse bee becomes forager

What happens if honeybees do not revive queen substance?

Workers raise new queens

Workers may become aggressive

Colony organisation breaks down

What is a vector?

• Organisms that transfer disease between hosts

What is a reservoir host?

• Species that maintains infection in the absence of of other hosts

What is the difference between mechanical and biological transmission?

• Mechanical: pathogen carried on mouthparts

• Biological: pathogen develops inside vector

What causes bluetongue virus?

• Virus is spread by biting midges

• Mainly affects cattle and sheep

What are the signs of bluetongue?

• Fever

• Swelling

• Drooling

• Eye and nasal discharge

How does temperature affect bluetongue transmission?

Increases vector survival

• Increases biting rate

• Spreads virus development

• Raises transmission risk

What are the main drivers of biodiversity loss?

• Land use change

• Direct exploitation

• Climate change

• Pollution

• Invasive species

How does agriculture contribute to biodiversity loss?

• Habitat destruction

• Soil erosion

• Nutrient loss

• Reduced crop diversity

• Pollution

What is direct exploitation?

• Hunting

• Fishing

• Logging

• Plant harvesting

How does climate change affect species distributions?

• Species move to higher latitudes

• Species move to higher elevations

• Shift to cooler environments

Why is genetic diversity important?

• Helps species adapt

• Reduces extinction risk

• Small populations lose diversity faster

How do invasive species affect biodiversity?

• Outcompete native species

• Spread through human activity

• Can expand further with climate change

Why are insects important pollinators?

• Around 75% of flowering plants are insect pollinated

• Pollination supports food production and biodiversity

How do insects improve biological control?

• Predatory insects eat pests

• Reduce need for pesticides

• Help control slugs, snails and crop pests

What is the biggest clause of insect decline?

• Habitat loss from intensive agriculture