xerophytes and hydrophytes

Question 1

what is a xerophyte?

Answer 1

A plant that is adapted to live in dry conditions

Question 2

What conditions can xerophytes survive in?

Answer 2

They are able to survive where soil water is in short supply and/or environmental conditions promote excessive rates of transpiration.

Question 3

what is a xeromorphic feature?

Answer 3

An adaptation which helps to significantly reduce evaporating losses of water and maximises water absorption

Question 4

What adaptation allow plants to normally reduce the loss of water by transpiration?

Answer 4

• A waxy cuticle on the leaf will reduce water loss due to evaporation through the epidermis
• The stomata are usually found on the underside of the leaf, not on the top - this reduces evaporation due to direct heating from the sun
• Most stomata are closed at night when there is no light for photosynthesis
• Deciduous plants lose their leaves in winter when the ground may be frozen - therefore making water less available - and when temperatures are too low for photosynthesis

Question 5

what are examples of common adaptations xeromorphic plants have in order to reduce water loss from their leaves and maximise water absorption?

Answer 5

• a reduction in the surface area to volume ratio of leaves as seen in the cactus and pine leaves
• the inward rolling of leaves to protect the stomatal surfaces and to reduce the surface area exposed to the environment
• The presence of hairs for trapping water vapour and reducing the water potential gradient between the leaf and the atmosphere
• Thick cuticles and sunken stomata reduces evaporative losses
• shallow extensive root systems for maximising water absorption in areas of low rainfall

Question 6

Give an example of a xerophyte:

Answer 6

Cacti are examples of xerophytes they display xeromorphic adaptations which help for surviving hot, dry environments where transpiration rates are high and water availability is low

Question 7

give 4 examples of the xeromorphic adaptations of cacti:

Answer 7

1. leaves are reduced to spines, minimising the exposed surface area and the number of stomata through which transpiration losses occur
2. The large, swollen stem contains chlorophyll in the epidermis, compensating for the reduced amount of chlorophyll available within the leaves for photosynthesis
3. The shallow, extensive root system displays a large surface area for rapid water absorption in an environment where rainfall is scarce; water absorption occurs before the water leaches away through the sandy soil
4. in contrast, some desert cacti possess very deep roots as an adaption for tapping into the available water that has leached through the sandy soil

Question 8

give an example of a type of xerophyte that inhabits sandy shores and dunes, where extremes of temperatures and harsh windy conditions promote water loss

Answer 8

• Marram grass

Question 9

give examples of the xeromorphic adaptations that marram grass have:

Answer 9

• leaves that can roll up to expose a tough waterproof cuticle to the air outside
• thick waxy cuticle to reduce water evaporation from the surface
• Rolling the lead traps humid air inside the leaf
• hairs trap water vapour = thus helping to reduce the water potential gradient - so less transpiration
• stomata are sunken - these trap water vapour near the stomata

Question 10

what is a hydrophyte?

Answer 10

A hydrophyte is a plant that is adapted to live in water

Question 11

What are benefits and challenges of living in water for hydrophytes?

Answer 11

Hydrophytes have easy access to water, but are faced with other issues such as getting oxygen to their submerged tissues and keeping afloat (they need to keep their leaves in the sunlight for photosynthesis)

Question 12

give an example of a hydrophyte:

Answer 12

A water lily

Question 13

give examples of the adaptations water lilies have:

Answer 13

1. the leaf has many air spaces - this keeps the leaves afloat so they are in the air and can absorb sunlight
2. the leaf stem has many large air spaces - this helps with buoyancy but also allows oxygen to diffuse quickly to the roots for aerobic respiration
3. the leaf has stomata on the upper epidermis - this means the stomata are exposed to the air allowing gaseous exchange

Question 14

what issues do hydrophytes face regarding transpiration?

Answer 14

transpiration is the loss of water vapour from the surface of the leaves but water will not evaporate into water or the air as it has very high humidity

Question 15

What are the effects if water cannot leave the plant?

Answer 15

the transpiration stream stops and the plant canot transport mineral ions up th leaf

Question 16

what adaptations do hydrophytes have to overcome difficulties with transpiration?

Answer 16

• many hydrophytes contain specialised structures at the tip of their leaves called hydathodes
  hydathoses are structures that release water droplets which may then evaporate from the leaf surface

Question 17

describe the structure of the specialised structures which release water droplets from the leaf surface?

Answer 17

these are openings like stomata. however, they always remain open and do not contain guard cells