Biology 2.5 - Transport systems in plants

• What is the transpiration process?

  1. Water enters the roots via osmosis
  2. Water travels through the root tissue by osmosis until it reaches the xylem
  3. The xylem transports water up the stem to the leaves
  4. The water moves through the leaf cells by osmosis and exits the leaf through the stomata by evaporation
• How the xylem works?

  It is a unidirectional process aided by a build-up of root pressure and pressure from evaporation.
• Root hairs function?

  To increase the surface area to absorb water and minerals
• What are xylem cells?

  Dead and empty - meaning they have no nucleus and no cytoplasm
• Xylem end walls?

  Xylem end walls are lignified - meaning they are hollow, impermeable tubes
• What does the lignin do?

  Provides structural support
• Water moves from the xylem to the air spaces by evaporation. In the air spaces it evaporates to form water vapour
• What are stomata?

  Pores/small openings on mainly found of the underside of the leaf epidermis
• Why can stomata close at night?

  Stomata can close at night if there is too much water loss
• What do guard cells control?

  The opening and closing of the stomata
• When guard cells become turgid...?

  The cells expand and the stomata opens
• When guard cells become flaccid...?

  The cells straighten and the stomata are mostly or fully closed
• Where are the most stomata found?

  The underside of the leaf
• What is the function of the phloem?

  The transport of sugars
• Is the phloem unidirectional or bidirectional?

  The phloem is bidirectional
• What is sugars traveling through the phloem called?

  Translocation
• What are the three parts of the phloem?

  Sieve tubes, sieve plate (end walls) and the companion cell
• How many sieve tubes are there?

  Multiple
• Sieve tubes run parallel to each other
• The companion cell is attached to one side of the sieve tube
• The sieve tube does not have a nucleus
• What controls the sieve tube?

  Companion cells
• What does a potometer measure?

  A potometer measures the rate of transpiration
• How does a potometer work?

  As water evaporates from the leafy shoot, water is drawn through the cut stem from the capillary tube, so the air bubble moves along.
• The faster the rate of transpiration, the faster the bubble moves
• Potometer precautions?

  • Plant shoot must be healthy
  • Leaves must be dry
  • The last 2-3cm of shoot must be cut off
  • The apparatus must be set up underwater
  • There must be no air bubbles
  • It must be airtight
• Why must the end of the shoot be cut off?

  The end of the shoot must be cut off because gas may have entered the stem, creating an airlock in the xylem
• Why must a potometer be set up underwater?

  To prevent air bubbles from entering the xylem
• What effect does the wind speed increasing have on transpiration speed?

  Increases the transpiration speed because the leaf cells lose more water because there is a higher concentration gradient
• What effect does the humidity increasing have on transpiration speed?

  Decreases transpiration speed because the concentration gradient decreases as there is more water vapour in the atmosphere, leading to the plant losing less water
• What effect does the temperature increasing have on transpiration speed?

  Increases transpiration speed because evaporation speed is increased and the plant loses more water
• What effect does the leaf surface area increasing have on transpiration speed?

  Increases transpiration speed because more stomata means more transpiration
• What are a plants organs?

  Roots, stems and leaves
• The inner walls are thicker and less elastic than the outer walls of a guard cell
• Name the types of leaf cells, from top to bottom of the leaf?

  Upper epidermis

  Palisade mesophyll

  Spongy mesophyll

  Xylem + Phloem

  Lower epidermis

  Guard cells

  Stomata
• Describe the structures and processes involved as water moves through the plant from the soil to the air?

  1. Water enters the root hairs by osmosis
  2. Water travels up the xylem
  3. Water travels to the stomata and diffuses out of the cell