Halophytes

Question 1

what are the structural adaptations of Halophytes ?

Answer 1

• Aerial root systems called pneumatophores
• Filtration structures in roots
• Salt glands

Question 2

what are the physiological adaptations of halophytes?

Answer 2

• Concentrates and stores salts in vacuoles
• Accumulates salts in leaves or bark.

Question 3

how does an aerial root system called pneumatophores work and give an example

Answer 3

aid in respiration. the muddy oxygen-poor soils that characterise these areas do not hold enough oxygen for these trees to effectively respire. oxygen diffuses into the spongy tissue of the pneumatophores. they grow upwards out of the water or mud or reach the air. e.g. mangroves

Question 4

how does filtration structures in roots work and give an example.

Answer 4

Prevent salt from entering their roots. Mangroves have an ultrafiltration system that can filter approximately 90% of sodium ions from the surrounding salt water. the three layers of the filtration system surrounding the roots trap sodium ions but allow water to pass through as it is pulled into the xylem. e.g. mangroves

Question 5

how do salt glands work and give an example

Answer 5

salt is directed to plant surfaces, where salt glands secrete salt to reduce salt content in the plant. e.g. mangroves

Question 6

how does concentrates and stores salts in vacuoles work and give an example

Answer 6

stores salt in the vacuoles of the fleshy stem segments or ‘beads’, which can have salt concentrations of 30-45%. the salt in the beats becomes highly concentrated, and they shrivel, die then drop off. this allows the rest of the plant to remain healthy. e.g. samphire, an Australian succulent.

Question 7

how does accumulates salts in leaves or bark work and give an example

Answer 7

salt is directed to older leaves or bark, where is accumulates. The leaves or bark eventually die and drop off, removing the salt from the plant. e.g. Samphire, and Australian succulent.

Question 8

how does a thick, waxy cuticle aid in water retention

Answer 8

structural
Provides a waterproof covering preventing evaporation of water
Transpiration through stomata only – regulated
E.g. Mulga, Eucalypts

Question 9

how do Upward Sloping Leaves & Branches aid in water retention

Answer 9

structural
= Tusic Shape
Water/rain runs down leaves, branches and stems, concentrated around roots at base of plant.
Also, to a lesser degree, reduces direct sunlight = less heat = less transpiration
Eg. Mulga

Question 10

how does a Stomatal Closure aid in water retention?

Answer 10

structural
Guard cells shrink, closing stoma, during times of low water (you already know about this one)
Reduces transpiration

Question 11

how do curling leaves aid in water retention?

Answer 11

structral
Leaves curl over trapping moist air = less transpiration
Fewer stomata directly exposed to external environment.
E.g. Porcupine grass
Spinifex

Question 12

how do Ephemerals aid in water retention

Answer 12

structural
Plants with a very short life-span.
Seeds only germinate after sufficient rain.
Then grow, flower and seed while conditions are favourable.
Eg. Gunniopsis intermedia

Question 13

how do Deciduous plants reserve water

Answer 13

structural
Lose their leaves when water is not available.
Eg. Autumn fagus

Question 14

how has a Shiny cuticle / Hairy Leaves aid in water retention?

Answer 14

structural
Increase reflected light = less heat = less transpiration.
Eg. Magnolia

Question 15

how do Vertically Hanging Leaves aid in water retention?

Answer 15

Structural (some say Behavioural)
Less SA to sunlight = less heat = less transpiration
Water/rain runs down leaves, dripping around roots at base of plant.
Eg. Eucalypts

Question 16

how do needle shaped leaves aid in water retention

Answer 16

structural
Less SA to sun
Eg. Pines

Question 17

how do extensive roots aid in water retention

Answer 17

structural
Spread thoroughly just under the surface to absorb maximum water (even dew)
Eg. Spinifex
+Grass tree

Question 18

how does a sunken stomata aid in water retention?

Answer 18

structural
Stomata recessed (or enclosed in cavity) allows small pocket of trapped water vapour
Eg. Some cacti

Question 19

how does stomata on the underside of the leaf aid in water retention ?

Answer 19

Structural
Less exposure to direct sunlight
Eg. Most plants

Question 20

how does a reduced leaf size aid in water retention

Answer 20

Structural
Decrease SA = reduced transpiration
Eg = Geraldton Wax

Question 21

important things to know about halophytes

Answer 21

Plants that survive in saline environments are termed halophytes
Most halophytes prefer saline conditions but can survive in freshwater environments
Most halophytes are restricted to saline environments

Question 22

morphological adaptations on the leaves of halophytes

Answer 22

Leaves are thick and their surfaces are reduced.

Question 23

morphological adaptations on the stem of halophytes

Answer 23

Well developed aerial stem and much branched.
The stem ranges from soft to hard woody type.

Question 24

morphological adaptations on the roots of halophytes

Answer 24

Tap root system is not much elaborate and deeply penetrating. In many cases, roots are negatively geotropic.

Question 25

rate of transpiration in halophytes adaptation

Answer 25

Like xerophytes, the rate of transpiration is checked by various kinds of morphological and anatomical modification of leaves

Question 26

gas exchange of halophytes

Answer 26

Gases exchange of the aerial plant parts takes place normally but the respiration of underground parts i.e. roots take place by the formation of negatively geotropic roots known as pneumatophores.

Question 27

absorption of water for halophytes

Answer 27

Absorption of water and mineral salts takes place slowly and selectively by the elaborate root system.

Question 28

what are the physiological features to discuss with xerophytes and halophytes?

Answer 28

- rate of transpiration - gas exchange - absorption of water

Question 29

Explain two distinctly different adaptations of halophytes to high-salt environments.

Answer 29

A definition of halophyte and their typical environment: Halophytes are plants that are able to survive in environments of high salt concentration, e.g. mangrove trees. A explanation of TWO of the following adaptations: Store salt in vacuoles in root cells: salt concentration in the cell exceeds that in soil, thus water moves into the root. Accumulate salt in leaves/bladders/salt glands/bark: discard salt/leaves/bladders which reduces the amount of salt in plant. Store salt in cell vacuoles: removes salt from cell cytoplasm which stops salt from interfering with cell function. Accumulate/store water in leaves/some parts of plant: dilutes salt content of cells in these parts of plant and provides a water store for drier periods. Prevent salt entering/regulate amount of salt: filtration mechanism at roots which avoids the plant having to deal with excess salt.