Plant Structure and Function

Types of Plant CellsParenchyma

Thin flexible cell walls.

2 main functions – storage and food production.– Large vacuole

stores water, starch and oils.

– Can contain many chloroplasts.

Types of Plant CellsCollenchyma

Typically long cells. Unevenly thickened

cell walls.– Thin parts can

stretch and grow. Provide support for

surrounding tissue. ie. – tough strands

in celery.

Types of Plant CellsSclerenchyma

Thick and rigid. Used for support Two types: fibers and

stone cells.– Fibers – long thin

strands, support, strength, vascular tissue.

– Stone cells – circular cells

Gritty texture of pears Fruit pits

Plant TissuesDermal or Epidermis

Flattened parenchyma cells cover and protect plant like skin

Produce a waxy cuticle – prevents water loss.

Plant TissuesDermal or Epidermis

Contain stomata: openings that control gas exchange.– Guard cells control

opening and closing.

Plant TissuesDermal or Epidermis

Root hairs: extensions of cell that help absorb water and minerals.

Plant TissuesDermal or Epidermis

Trichomes: hair like – give fuzzy texture– Reduce

evaporation.– Some protect by

secreting toxic substances.

Plant TissuesVascular Tissues

Transport food minerals and water through the plant.

Two types:– Xylem – Moves water and minerals from

roots to rest of plant.– Phloem – Transport sugars and organic

compounds from leaves to rest of plant.

Plant TissuesXylem

Two types Tracheids: In conifers.

– Tubular, tapered ends, dead at maturity.

– Cell walls have pits for water flow across cells.

Vessel elements: In Anthopytes.– Wider and shorter.– Openings in end walls for

water flow through cells.

Plant TissuesXylem

Plant TissuePhloem

Transport sugars and organic compounds.

Living, tubular cells. Phloem cells are called

sieve tube members. Have cytoplasm but no

nucleus or ribosomes. Companion cells – next

to each sieve tube member. Help manage transport.

Plant TissuesGround Tissue

All other tissues Mostly parenchyma Functions: photosynthesis, storage,

support.– In stems and roots: have large vacuoles

to store starch and water.

Plant TissuesMeristematic Tissues

Region of actively dividing cells. Small, round, with large nuclei. Apical meristems:

– At tips of roots and stems.– Increase length.

Lateral meristems:– Cylinders of dividing cells in roots and stems.– Increase diameter.– Vascular cambium: produce xylem and phloem.– Cork cambium: produces tough covering for root

and stems.

Meristems

Roots Anchor, absorb water and minerals from soil. Some used for food storage (carrots) Two types

– Taproots: central fleshy with small branch roots. (carrots, beets)

– Fibrous roots: numerous branches from central point.

Root Variations Adventitious

roots:– Prop roots above

ground to support tall plants.

Aerial roots:– Cling to objects

to provide support.

Root Structure

Epidermis: outer layer.– Root hair: extension of single epidermal cell.– Absorbs water, oxygen and minerals.

Root Structure

Cortex: next layer.– Transports water and ions into vascular core.– Made of parenchyma cells

sometimes used for storage

Root Structure

Endodermis: forms waterproof seal around vascular tissue.– All water and minerals must pass through

endodermis cells.

Root Structure

Pericycle: just within endodermis.– Gives rise to lateral roots (offshoots of older

roots).

Root Structure

Xylem and phloem: center of root.– Transport of water, minerals and organic

materials through plant.

Dicot vs. Monocot Root

Dicot vs. Monocot Root

Root Growth Apical meristem

– Lengthens root Vascular cambium

– Increase diameter– Found between

xylem and phloem Root cap

– Layer of cells at root tip.

– Protection

Stems Transport, support and

storage. Some are Underground

– Corm: short, thick, surrounded by leaf scales. (gladiolus)

– Tuber: swollen underground stem with buds that sprout new plants. (potato)

– Rhizomes: (iris)

Stem: Internal Structure Vascular tissue arranged in bundles.

Dicot Monocot

Woody Stems Secondary

Growth: thickness from vascular cambium.– Xylem: wood –

causes growth rings.

– Bark: old phloem and cork cambium.

Stems – Material Transport Xylem: transports water from roots to leaves. Phloem: transports sugars, minerals, and

hormones.– Source: photosynthetic tissue – mostly leaves.– Sink: storage area (cortex of roots)– Translocation: movement from source to sink.

Leaf Variation Simple: blade no

divided Compound: divided

into leaflets Alternate: only one

leaf from a single point on stem

Opposite: leaves in pairs along stem

Whorled: three or more leaves occurring at same place on stem

Leaf Structure Vascular tissue in veins. Epidermis: outer layer of cells. Two layers of Mesophyll.

– Palisade mesophyll: Most photosynthesis.

– Spongy mesophyll: Loosely packed with irregular shaped cells. Air spaces for gas exchange: O2, CO2, H2O. Gases move in and out of stomata.

Transpiration Loss of water vapor through the stomata.

Leaf Venation Patterns Parallel – monocots Netlike – dicots

Leaf Modifications Cactus spines: leaves that reduce

water loss and protect plant. Bulb: short stem covered by large

fleshy leaves, modified for food storage.

Pitcher plant: modified to trap insects. Aloe vera: adapted to store water.

Plant Responses

Hormones

Tropisms

Nastic Responses

Plant Hormones Chemicals produced in one part of an

organism and transported to another to cause a change in growth or development.

Auxins: Hormone Promote cell elongation. (IAA) Indoleacetic acid.

– Produced in apical meristem.– Increases cell division and promotes cell

elongation. Weakens connections between cellulose

fibers in the cell wall allowing cells to stretch.

Auxin Auxins produced in apical meristem

inhibits growth of side branches. Remove stem tip – branches form

Gibberellins: Hormone Growth hormone. Stimulates cell

elongation. Also increases

rate of seed germination and bud development.

Cytokinins: Hormone Stimulate cell division or cytokinesis. Stimulate production of proteins

needed for mitosis. Produced in meristem of roots and

travel up xylem to rest of plant.

Ethylene: Hormone

A gas that speeds ripening of fruits.

Tropism Response to an external stimulus from

a particular direction.– Positive tropism: plant grows toward

stimulus.– Negative tropism: plant grows away from

stimulus.

Types of Tropism Phototropism: growth toward light.

– More auxin on side of stem away from light.

– Cell elongation on one side – dark side. Gravitropism: direction of plant growth

in response to gravity.– Stems up and roots down.

Thigmotropism: response to touch.– Tendrils of vine coil around objects.

Nastic Responses Response movement that is not dependent

on direction of stimulus. Mimosa Venus Flytrap