UNIT 1: Gas Exchange and Transport in Plants

When organisms increase in size

• SA:V decreases

  • distance from center to outside increases

  • need adapations to facillitate gas exchange

Adaptations in leaves for gas exchange

• Large surface area

• Thin tissue layers

• Permeable membranes

• Concentration gradient

• Moisture on exhchange surfaces that allow gases to dissolve and diffuse rapidly

Leaves are adapted for

Gas exchange, photosynthesis, prevent water loss

KNOW HOW TO DRAW AND LABEL A LEAF CROSS SECTION

I just did it

Waxy cuticle adaptations

covers epidermis, prevents water loss

epidermis adaptations

one thick cell that provides protection for mesophyl

Transparent, allowing light to hit mesophyll for photosynthesis

spongy mesophyll

Surrounded by air spaces that increase surface area for gas exchange

air spaces in spongy mesophyl

facillitate gas exchange

stomata

porees that allow gases to be exchanged. On the lower epidermis. Open and close via guard cells

veins

Support the leaf

Xylem- Water and minerals up the roots

Phloem- Nutrients up and down the plant (amino acids and sucurose)

Transpiration

Movement of water through a plant and evaporation into the atmosphere from aerial parts of the plant such as leaves

Transpiration is an inevitable consequence of

gas exchange, water in mesophyll evaporate and diffuse through open stomata

Water movement in transpiration

High concentration in air space of spongy mesophyll to low concentration of particles in the atmosphere

Stomatal Density

Mean # of stomata/Area of FOV mm³

4 main factors that effect transpiration

• Light Intensity- more light, more photosynthesis, more transpiration. Still transpiration in the dark

• Air Flow- the windier the better, however too much wind can close it

• Humidity- low humidity, more transpiration

• Temperature- the warmer the higher the rate

Xylem in transpiration

water enters roots via osmosis to the leaves via xylem vessels, it is then drawn out of the xylem vessels and through cell walls via capillary action generating tension. Use also cohesion and adhesion.

Xylem vessels

long hollow tubes formed by xylem cells, stacked on top of each other, dead, hollow cells with no end walls.

Adaptations of xylem

• No end walls

  • allow column of water to move up teh plant

• No cell contents of plasma membrane

  • allow continuous, uninterupted flow of water

• Pits

  • allow water to move between xylem and adjacent cells

• Lignin

  • strenghens wall of xylem allowing the vessels to risist the tension created by transpiration

DRAW A DICOT STEM

Drew ur stem

Dicot stem- epidermis

provides protection for stem

Dicot stem- cortex

structural support, stores starch in the root

Dicot stem- vascular bundles

contains veins, transport materials, xylem and phloem. Phloem—→peripherary

DRAW A DICOT ROOT

drew the root

Root pressure summary

• positive pressure potential

• generated to cause water movement in roots and stems when transport in xylem due to transpiration is insufficeint

  • IE High humidity

  • Spring before leaves open

root pressure process

• mineral ions actively transported through casparian strip of endodermis into the xylem

  • low water potential in xylem

• Water moves into xylem by osmosis

  • positive root pressure

• Root pressure allows this water to move up xylem when transpiration rates are low (ie high humidity, absense of leaves etc)

Roots absorb water

water enters the roots of a plant due to high mineral ion solute concentration within root cells

Ways water moves from root hairs to xylem

Symplastic Pathway

Apoplastic Pathway

Symplastic Pathway

Water moves through cytoplasm of adjacent cells via osmosis

Apoplastic pathway

water moves through cell walls of plant cells via capillary action

Translocation

Moves nutrients (sucrose, amino acids) up and down the stem of a plant via phloem tissue`

Phloem tissue

transports nutrients such as sucrose and amino acids up and down the stem of the plant

• comprised of companion cells and sieve tubes

• Cytoplasm of sieve tube and companion cells linked through plasmodesmata

Sieve tubes

• long and narrow formed by sieve element cells

• Adapted to their function of transporting nutirents up and down the plant

Adaptations of sieve tubes

• reduced cytoplasm and organelles + no nucleus

  • allow sap movement

• Plasma membrane w/ protein pumps

  • active transport

• Sieve plates

  • pores (appearing like a sieve in the cell walls between cells) allowing cell sap containing nutrients to flow from cell to cell

• Plasmodesmata

  • allows direct connections between cytoplasm of companion cell and sieve tube

Companion cells

Provide metabolic support for sieve tube element cells, thus every STEC is connected to the cytoplasm of a companion cell via plasmodesmata

Adaptations of companion cells

• plasmodesmata- connect cytoplasm of companion cells to cytoplasm of STEC

• Large number of mitochondira to provide suffienent ATP for active transport of nutrients in the phloem tissue

• Contain transport proteins that load nutrients into sieve tubes

Translocation moves_________

Nutrients from source (where they're produced) to sink (where they are stored and used)

At the sink (roots)

sucurose is actively transported into root cells to be used for respiration or to be stored as starch

Storage tissue can also be

sources, and the stored starch is converted to sucrose and transported to sinks such as growing tissues