Bio 3031 Plant Responses To Their External Environment

Question 1

Habitat

Answer 1

The place where an organism lives

Question 2

Ecosystem

Answer 2

A community of living organisms (biotic environment) together with non-living factors (abiotic environment), and the nutrient cycles and energy flows that connect all.

Question 3

Stimulus

Answer 3

A stimulus is a change in the environment that causes a response in an organism

Question 4

Adaptation

Answer 4

An adaptation is an inherited characteristic that enables an organism to survive and reproduce in its habitat. Adaptations may be structural, behavioural, or physiological

Question 5

Biotic environment

Answer 5

The biotic environment is the influences of living organisms on each other.

Question 6

Abiotic environment

Answer 6

The abiotic environment is the non-living influences on an organism.

Question 7

Ecological niche

Answer 7

The ecological niche is a description of how the organism feeds, the opportunities provided by the habitat and the adaptive features of the organism which enable it to take advantage of these opportunities.

Question 8

Tolerance

Answer 8

An organism’s ability to survive variation in its environmental conditions.

Question 9

Acclimitisation

Answer 9

The ability of an organism to adjust its tolerance limits or optimum range in response to slow changes in its environment.

Question 10

Ecological niche

Answer 10

A description of how the organism feeds, opportunities provided by the habitat and the adaptative features of the organism that allow it to take advantage of these opportunities.

Question 11

Ecological niche includes interaction with biotic and abiotic environment such as :

Answer 11

• its relationship with other organisms
• its reproductive strategies to ensure the species survives
• the resources and opportunities rovided by the habitat
• the adaptations its has which enable it to take advantage of these opportunities

Question 12

Gause’s principle

Answer 12

States that no two species with identical ecological niches can co-exist for long in the same place.

Question 13

Structural adaptations

Answer 13

Features of body structure.
Such as, a snail’s shell for protection. A bird’s wing for flight. A cat’s claw to catch prey. A plant’s leaves to trap sunlight for photosynthesis. A plant’s flower to attract pollinators.

Question 14

Behavioural adaptations

Answer 14

Types of behaviour that helps an organism to survive.
Such as male birds feeding female birds while sitting on the nest. A hedgehog curling into a ball when threatened. A possum’s nocturnal activities.

Question 15

Physiological adaptations

Answer 15

Chemical or physical adaptations.
Such as, human keeping their body temperature at 37*C despite changes in the temperature of external environment. Pale skin tans when exposed to sun over long periods. Callouses on hands and feet in response to repeated contact or pressure.

Question 16

Abiotic environmental factors.

Answer 16

Physical factors that can act as stimuli to which the organisms need to respond. All factors like these are non-living abiotic influences.
-soil type
-intensity and direction of light
-availability and amount of water
-salinity and clarity of water
-availability and quality of air
-pressure (altitude)
-average and range of temperature
-effect of gravity
-velocity and direction of wind
-presence of chemicals and nutrients

Question 17

Biotic factors may be

Answer 17

Intraspecific - between members of the same species
Interspecific - between members of different species

Question 18

Intraspecific

Answer 18

Between members of the same species.
Examples of Intraspecific biotic factors are competition for resources such as
- food, water, light, space, nesting sites and mates.
-Cooperation strategies within species for defence, hunting and survival.
- Aggressive interactions to establish hierarchies and defend territories.
Can be intense as all individuals have the same requirements for resources.

Question 19

Interspecific

Answer 19

Between members of different species
Competition occurs if different species have similar requirements for any resource. Interspecific biotic factors are competition for resources such as
- food, water, light and space
- exploitation of one species by another, such as parasitism and predator/prey interactions
- mutualism, which is an association between species for their mutual benefit

Question 20

Competition

Answer 20

May be Intraspecific or Interspecific and may be either through interference in the growth of other species or through exploitation of other species.
Competition is most typically considered the interaction of individuals that vie for a common resource that is in limited supply, which leads to a change in fitness when the organisms share the same resource.

Question 21

Resources that plants compete for:

Answer 21

-sunlight
-water
-nutrients in soil
-carbon dioxide from atmosphere
-space to grow

Question 22

Why do plants compete with each other for resources?

Answer 22

Plants compete with each other for resources in order to survive in the environment. They have developed cooperative strategies that help them survive. May be symbiotic associations with other plants.

Question 23

Stratification

Answer 23

The vertical layering of plants.
The plants demanding lots of light grows in the canopy and those that require less light grows in the layers below.

Question 24

Give examples of how plants compete

Answer 24

• Main way plants compete for sunlightis to grow towards the light, overshadowing other competing plants nearby and slowing their growth.
• utilising the available resources more quickly than neighboring plants.
• growing longer roots or more more xtensive root system to take advantage of water supply, or being better able to tolerate adverse conditions.

Question 25

Competition between plants, abiotic or biotic?

Answer 25

While the available respurces are abiotic environmental factors, the competition between plants for these resources is biotic, as the plabts are living elements of the environment.

Question 26

Allelopathy

Answer 26

The production of toxic chemicals that inhibit growth.

Question 27

Explain examples of allelopathy

Answer 27

Desert plants use allelopathy to ensure no plants grow nearby so that their roots can use the scarce water resource to their advantage.
Plants such as wetland species, grasses, tobacco, rice and pea plants are known to produce root allelotoxins to reduce competition with neighboring plants.

Question 28

Exploitation

Answer 28

The use of natural resources of economic growth. Some species actively exploit neighbours in order to compete for resources.
- e.g. long vines in a forest growing up trees to reach sunlight for photosynthesis is nie exploiting the trunks.

Question 29

Example of allelopathic cooperation between plants

Answer 29

The roots of marigold plants secrete a chemical that kills parasitic nematodes (roundworm that damages plants). Nematodes cause swellings on the roots which stunt the plants’ growth and commonly lead to death. Producing a toxic chemical is a form of allelopathy, however, usually the chemicals are detrimental to the growth of other plants, here the chemical produced is beneficial as it kills nematodes.

Question 30

Example of cooperative strategies

Answer 30

Some fruit trees cannot be self polinated. This means that they need another tree of the same species to grow nearby for pollination. This way, both trees benefit from cross pollination and can produce flowers and fruit with increased genetic diversity as a result.

Question 31

Symbiosis

Answer 31

Any relationship or interaction between two dissimilar organisms

Question 32

Mutualistic

Answer 32

When two organisms of different species work together, each benefiting from the relationship.

Question 33

Physical defenses

Answer 33

• thorns or spines
• bark, gum, thick waxy cuticles
• divarication
• seed masting

Question 34

Divarication

Answer 34

Plants branch repeatedly and produce a tangle of stems with the outer branches having smaller and fewer leaves than the inner branches. Stems are often tough and difficult to break.

Question 35

Seed masting

Answer 35

Every few years all trees of same species release all their seed simultaneously.
- with so many seeds available, not all of it will get eaten by seed eating animals and some will survive to germinate.
- as there are not enough seeds in the intervening years to support a large population of seed eating animals, there is less chance of seeds being eaten during a mast year

Question 36

Chemical defenses

Answer 36

-produce unpalatable chemicals
-herbs and spices produce essential oils
-morphine in opium poppies
-nicotine in tobacco
-monofluoroacetate as a natural defense against browsing mammals
-toxin 1080 human made chemical used against possums

Question 37

Life saving chemicals

Answer 37

• pyrethrins (very poisonous to insects and stop them from eating their leaves, however some caterpillars can eat them with no harm by detoxifying the chemical)
• sesamin (works against the chemical in caterpillars that detoxify pyrethrin and therefore overrule this chemical)

Question 38

Plant communication

Answer 38

Plants communicate with each other through chemicals.

Question 39

Ethylene (ethene)

Answer 39

-Leaves damaged by pathogens or insect attack produce defensive molecules such as ethylene.
-It signals other plants to activate plant defense genes.
-signalling molecules serve as a warning to other plants of the same species that they are under herbivore attack.
-neighboring plants are then stimulated to produce their own chemical responses against herbivores.

Question 40

Explain how a willow tree protects itself from attack by insects.

Answer 40

When a willow tree is attacked by insects, it produces a chemical called salicin in response. The chemical travels through the tree and induces it to produce pathogenic chemicals (pphytoalexins) that protect the tree from further attack.
Some of the volatile salicin becomes airborne and is sensed by other willow trees nearby.
They are warned of the insect attack and start to produce defensive chemicals too.

Question 41

Explain carnivorous plants

Answer 41

-Carnivorous plants are plants that attack. -These plants usually grow in bogs which means that they lack essential minerals such as nitrogen.
-Plants overcome mineral deficiency by devouring insects and digesting their bodies.
-venus fly trap, pitcher plants and sundews are examples of a carnivorous plant
-some have sensitive hairs that sense insects and cause the plant to shut rapidly (venus fly)
-some are shaped in a way that insects can’t escape once they are in (pitcher)
-some have sticky hairs (sundews)
-once the insect is trapped, digestive juices are released by the plant to digest the prey making its minerals available to the plant

Question 42

Tropism

Answer 42

-A tropism is a growth response made by plants to external stimuli in their abiotic environment.
-The direction of the stimulus determines the direction of the growth response.
-The tropic response may be POSITIVE > plant grows toeards the stimulus or NEGATIVE > plant grows away from stimulus.
-cannot be reversed

Question 43

Nastic (nasty) response

Answer 43

-A non-directional movement of part of a plant in response to an external environment stimulus.
-Made to the intensity of the stimulus rather than to the direction.
-reversible

Question 44

Give examples of tropism

Answer 44

• light (phototropism) where a plant’s stem grows towards the light and so it is positively phototropic. OR a plant’s roots grow down into the soil away from the light and so the roots are negatively phototropic
• water (hydrophotopism)
• temperature (thermotropism)
  -gravity (geotropism or gravitropism)
  -sun (heliotropism)
  -chemicals (chemotropism)
  -touch (thigmotropsim)
  -current (rheotropism)

Question 45

Give examples of nastic responses

Answer 45

-plants make nastic responses to the intensity of light, temperature and humidity.
-nastic responses are turgor responses
-flowers closing at night and opening during daytime (photonasty or thermonasty)
-haptonastic movements in the venus fly trap

Question 46

Plant hormones

Answer 46

Chemicals that are produced in one area of the plant and transported to other areas where they produce an appropriate growth response.

Question 47

Explain receptor cells

Answer 47

Receptor cells in the leaves, shoots and roots detect the presence of the light and gravity stimuli and then respond appropriately to these stimuli by producing hormones.

Question 48

Effector

Answer 48

The region of the plant where the growth response occurs.

Question 49

Auxin

Answer 49

-A plant hormone that affects groeth and development.
-more auxin > faster growth
-no auxin > no growth
-root growth is inhibited by high concentrations of auxin
-roots are more sensitive to auxin concentrations than stems
-seeds use gravity receptors that move to the lower side of the cell and affect the distribution of auxin so that there is more auxin on the underside

Question 50

Apical dominance

Answer 50

Apex (tip) produces most auxin, so the plant grows upwards.
Laterals (side shoots) do not grow.
Auxin inhibits laterals growth.
If tip of laterals are cut off, the sode shoots will develop and grow bushier.

Question 51

What are the five major groups of plant hormones involved in plant growth.

Answer 51

-auxins
-gibberellins
-cytokinins
-abscisic acid
-ethylene gas

Question 52

Auxin (read through)

Answer 52

-Promotes stem elongation.
-Controls cell enlargement.
-Causes apical dominance by suppressing growth of lateral buds.
-Stimulates cell division in cambium (secondary vascular growth).
-Stimulates root initiation.
-Suppresses root elongation.
-Delays onset of leaf fall.
-Delays fruit ripening.
-Stimulates growth of flower parts.

Question 53

Gibberellin (read through)

Answer 53

-Promotes stem elongation.
-Delays dormancy and leaf fall.
-Breaks dormancy in seeds and buds.

Question 54

Cytokinin (read through)

Answer 54

-Stimulates cell division.
-Promotes growth of young fruit.
-Balances root and shoot growth.

Question 55

Abscisic acid (read through)

Answer 55

-Inhibits growth, produces winter dormancy.
-Induces fruit fall.
-Promotes seed dormancy.
-Acts on guard cells; produced in response to water stress and promotes closing of stomata.
-(The effects of abscisic acid are generally the opposite of those of auxins, gibberellins and cytokinins

Question 56

Ethylene gas (read through)

Answer 56

-Induces fruit to ripen
-Aids leaf fall

Question 57

Stimuli may be …

Answer 57

Stimuli may be endogenous (internal) or exogenous (external) to a plant.

Question 58

What rhythm do plant responses follow

Answer 58

Plant responses may follow a circadian rhythm

Question 59

Photoperiodism

Answer 59

It describes the plants’ biological response to the relative amounts of light and darkness in any 24-hour period (photoperiod).

Question 60

How does plants sense the photoperiod

Answer 60

By using phytochromes

Question 61

Circannual

Answer 61

Some plants show yearly rhythms as they : •produce buds and new leaves in spring,
•flower at one time of the year (often spring or summer),
•lose their leaves in autumn and
•go dormant at other times (usually in winter)
•these plants are following a yearly cycle of growth and development.

Question 62

Annual plants …

Answer 62

Grow, flower and set seed during one year (e.g. petunias and pansies)

Question 63

Biennial plants…

Answer 63

Groe leaves and store food in the first year and flower in the second year (e.g. carrots and foxgloves)

Question 64

Perennials…

Answer 64

Grow, and flower every year for a number of years. Many die down and become dormant, usually over winter, then grow new leaves in spring (e.g. dahlias and lavender)

Question 65

Ephemerals…

Answer 65

Desert plants that germinate, grow, flower and set seed in a few weeks, after rainfall. They contain a chemical that inhibits the seeds from germinating until sufficient rain has fallen. Then carry out their life cycle quickly, before the desert dries out again.

Question 66

Exogenous

Answer 66

A factor of stimulus that originates outside an organism.

Question 67

Endogenous

Answer 67

A factor or stimulus that originates within an organism.

Question 68

Plant responses to day length

Answer 68

-change in leaf colour
-leaf drop in deciduous trees in autumn
-tuber and bulb formation
-start of winter dormancy
-germination of some seeds like lettuce
-bud break of fruit tree in spring
-grass tillering
-change from leaf development to flower development

Question 69

What are phytochromes and two forms

Answer 69

Phytochromes are protein pigments in plants that are sensitive to red and infrared light.
Two interchangeable forms exist:
-pr which absorbs red light
-pfr hich absorbs infrared light

Question 70

What is the relationship between pr and pfr

Answer 70

-Each form changes back to the other when it absorbs light.
-On absorbing light in the daytime, Pr converts to Pfr.
-At night, Pfr reverts back to Pr.

Question 71

What is pfr

Answer 71

Pfr is the biologically active form that acts as a switch to turn on plant responses.

Question 72

Why are phytochromes important

Answer 72

Phytochromes are important in the control of flowering.
They also act in :
-germination of seeds, which need brief exposure to light before they germinate
-stem elongation (infrared light)
-leaf expansion (red light)
-growth of side roots (infrared light)

Question 73

Day neutral plants

Answer 73

Plants that flower when they are mature, whatever the photoperiod is.

Question 74

What is the critical factor

Answer 74

The length of the dark period that is the critical factor.

Question 75

LDP and SDP

Answer 75

Question 76

Vernalisation

Answer 76

The exposure of a plant to a period of low temperature to promote later growth and flowering. The stimulus is picked up by the mature stem apex or by the embryo of the seed, not the leaves, as in photoperiodism.

Question 77

Which plants require vernalisation

Answer 77

Short-day plants
Long-day plants
Day-neutral plants.

However the lenght of chilling can vary from four days to three months, with temperatures around 4*C generally being most effective.

Question 78

Explain Vernalisation and gibberellins

Answer 78

During vernalisation, gibberellins increase.
Gibberellins can be used artificially on unvernalised plants to substitute for vernalisation.

Question 79

What is the importance of photoperiodism and vernalisation in plant survival.

Answer 79

-Both work to synchronize the reproductive behaviour of plants with their environment to ensure reproduction at the most favorable times of the year.
-It will ensure that members of the same species will flower at the same time
-It encourages cross pollination and cross fertilisation
-with advantages these bring in genetic variability

Question 80

What is dormancy in plants

Answer 80

-it occurs when growth and development in plants cease and the plants’ metabolic rates fall to a point which is only sufficient to keep the cells alive. (Normal winter state of most plants in temperature regions)

Question 81

How is dormancy brought about

Answer 81

-by light & temp acting through hormones
-winter buds in temp trees form as photoperiodic response to shortened days in autumn
-stimulus is perceived in leaves & hormones are produced
-produced hormones lead to build-up in chem abscisic acid.
-abscisic acid inhibits growth & induces leaf fall

Question 82

Extension of dormancy in plants

Answer 82

-storage organs involved when plant goes into a dormant state
-photoperiodism involved
-short days induce tuber formation in potatoes
-long days induce onion bulb formation

Question 83

Examples of temperature trees

Answer 83

Birch
Bees
Sycamore

Question 84

Storage organs in plants

Answer 84

Bulbs
Tubers

Question 85

Give the factors that can lead to abscission (leaf fall)

Answer 85

-lowering of light intensity
-drop in temperature
-shortening of day length
-water storage as result of drought conditions or freezing of water in the soil

Question 86

Explain, in short, leaf fall

Answer 86

As a result of buil-up in abscisic acid, a layer of weakened cells collects at base of petiole. Leaf eventually breaks off from the parents plant at this point. Most obvious in deciduous plants.