Higher Biology Adaptation Part 4 Adaptation 4 By

Higher Biology Adaptation Part 4

Adaptation 4 By the end of this lesson you should be able to: Ø Know what a xerophyte is. Ø Describe the problems that xerophytes face. Ø Describe how xerophytes are adapted to survive in Ø their environment. Ø Know what a hydrophyte is. Ø Describe the problems that hydrophytes face. Ø Describe how hydrophytes are adapted to survive in their environment. 2

Xerophytes ¡ ¡ Moorlands- exposed and windy Xerophytes are plants that have become adapted to survive in habitats where transpiration rates are very high. Examples of habitats are: Deserts- hot and dry 3

Xerophytes ¡ There are 3 categories of xeromorphic adaptations: Structural adaptationsreduce transpiration rate Structural adaptationsresisting drought Physiological adaptations 4

Structural adaptations To reduce transpiration rate: 1. Leaves have a reduced number of stomata. 2. Leaves have a thick cuticle. 3. Leaves can be rolled and/or hairy. 4. Leaves have sunken stomata in pits. 5. Leaves can be small and circular. 6. Leaves are reduced to spines. 5

Structural adaptations To reduce transpiration rate: Marram Grass (T. S. ) Rolled leaf Hairs Thick cuticle 6

Structural adaptations To reduce transpiration rate: Cactus surface Sunken stomata in pits Thick cuticle 7

Structural adaptations To resist drought: 1. Long roots. 2. Extensive system of superficial roots. 3. Storing water in succulent tissues. 4. Folded stems. 8

Physiological adaptations To reduce water loss: 1. Reversed stomatal rhythm- closed during the day and open at night. They take in CO 2 during the night and store it for use in photosynthesis during the day. 2. Ceasing vegetative activity during dry times- e. g. existing in a desiccated state (seed) and only germinating when water becomes available. ¡ Insert and complete the “Xerophytes” summary sheet. 9

¡ Hydrophytes are Hydrophytes plants that live either partially or completely submerged in water. Partially submerged e. g. water lily Completely submerged e. g. water milfoil 10

Hydrophytes ¡ These have evolved adaptations to help them survive in an aquatic environment. 11

Hydrophytes- adaptations Specialised leaves ¡ Submerged leaves have no stomata. ¡ Floating leaves have all their stomata on the upper surface. ¡ Floating leaves have long leaf stalks (petioles) to enable the leaves to move up and down in response to changes in water level. ¡ Submerged leaves are narrow or finely divided. 12

Hydrophytes Floating leaves- stomata on top surface e. g. water lily Narrow, finely divided leaves e. g. water milfoil 13

Hydrophytes adaptations Reduced Xylem: 1. Not required since water provides the support for submerged plants. 2. Any xylem is found at the centre of the stem- to allow flexibility in response to water movements. 14

Hydrophytes adaptations Extensive air spaces: 1. Store O 2 produced during photosynthesis for use in respiration. 2. Provide buoyancy for leaves- keeps them near the surface for maximum exposure to light. ¡ Insert and complete the “Hydrophytes” summary sheet. 15

Practice Questions ¡ 1. 2. Torrance TYK page 183 Q 1 -5 AYK page 184 Q 4 -6 16

Adaptation 4 Can you do it? Ø Know what a xerophyte is. Ø Describe the problems that xerophytes face. Ø Describe how xerophytes are adapted to survive in Ø their environment. Ø Know what a hydrophyte is. Ø Describe the problems that hydrophytes face. Ø Describe how hydrophytes are adapted to survive in their environment. 17