Biology - Unit 5: Plants

Vascular Plants

• plants with a vascular system (transporting water and nutrients)

Dermal Tissue

• outermost cell layers

• often with thicker cell walls - protects plant from injury, diseases, & predators

• covered with a waxy cuticle - prevents water loss

Epidermis

• dermal tissue in non-woody plants

Periderm

• dermal tissue in woody plants

• cork + cork cambium

Vascular Tissue

• transports water and nutrients

• supports the plant body

Xylem

• thick-walled cells, dead at maturity

• transports water one way

Phloem

• thin-walled cells, living at maturity

• transports nutrients from source to sink, goes both ways

Ground Tissue

• filler tissue between dermal and vascular tissue

• supports development, stores starch, and protects the plant body

Parenchyma

• thin-walled cells, living at maturity

• supports development

• stores starch

Collenchyma

• thick-walled cells, living at maturity

• supports development

• protects the plant body

Sclerenchyma

• cells with lignin in cell walls, dead at maturity

• protects the plant body

Meristematic Cells

• undifferentiated plant cells, rapidly dividing

• found in areas of growth

Cotyledons

• stores and supplies nutrients to the embryo

Monocots

• angiosperms with one cotyledon

Dicots

• angiosperms with 2 cotyledons

Leaves

• primary site of photosynthesis and gas exchange

• may offer protection from herbivores

Blade

• flat part of leaf

Petiole

• stalk that connects the leaf to the stem

Veins

• bundled xylem and phloem

• conducts carbohydrates to areas of growth or to the roots for storage

Venation

• pattern of veins

• monocot - parallel

• dicot - branched

Cuticle

• waxy, lipid layer

• prevents water loss

• protects against bacteria, moulds, and insects

Epidermis

• thin, flat cells that form the outer layer of tissues

• transparent to let light into cells below

• protects interior tissues

• produces the cuticle

Palisade Mesophyll Cells

• maximizes photosynthesis

Spongy Mesophyll Cells

• photosynthesis

• loosely packed to allow for gas exchange in leaf

Stomata (s. Stoma)

• opening for gas exchange

• more on the underside of the leaf

Guard Cells

• controls the opening and closing of the stoma

• water pressure in cell membrane controls guard cells

Stems

• connects roots to leaves - transport water and nutrients

• supports leaves and flowers - increase sun exposure and pollination

• store water and carbohydrates (some plants)

Herbaceous Stems

• photosynthetic

• thin epidermis

• monocot - scattered vascular bundles

• dicot - ring of vascular bundles

Wood

• made of xylem cells

Heartwood

• xylem cells that no longer transport water

• supports the tree

Sapwood

• transports water

• youngest xylem cells

Vascular Cambium

• meristematic region for xylem and phloem

Bark

• phloem + periderm

Cork

• outer layer that protects the tree

• prevents water loss

Cork Cambium

• meristematic region for cork

Roots

• anchors the plant

• absorbs water and nutrients other than carbohydrates

• stores water and carbohydrates

Taproot System

• has a taproot and may have lateral roots branching from it

• has root hairs

Taproot

• a large, main root

• goes deep into the soil

Root Hairs

• microscopic hair-like outgrowth from the epidermis that absorbs water and nutrients

• increases surface area for better absorption

Fibrous Root System

• many small roots, may have lateral roots

• has root

• tends to be more shallow than taproot system

Root Cap

• thick layer of cells that produce a slippery substance to penetrate the soil

• minimize damage to root cells

Root Cortex

• region of parenchyma cells beneath the epidermis

• stores carbohydrates

• transports water from epidermis to xylem

Endodermis

• innermost layer of cells in the root cortex

Casparian Strip

• waxy ring

• prevents water from leaking back into the cortex

Vascular Cylinder

• contains vascular tissue (xylem and phloem)

• central portion of the root

Monocot Roots

• center of parenchyma cells

• a ring of xylem cells and a ring of phloem cells

Dicot Roots

• xylem cells form a ‘X’ or star shape in the center of the root

• phloem cells in the center, surrounds xylem cells

Transpiration

• loss of water vapour from leaves and other aerial parts of the plant

• main driving force of xylem sap

Tracheids

• tapered at ends, overlaps each other

• has pits, allows xylem sap to travel between tracheids

Pits

• opening between cells, allows water to travel horizontally

Vessel Elements

• cylindrical, water flows vertically or horizontally

• has pits and perforations

Perforations

• holes between vessel elements that allows water to flow vertically

Root Pressure

• water pressure created in the roots

• not the major mechanism driving the ascent of xylem sap - only drives sap upwards a few meters

• some plants don’t create root pressure

Cohesion

• attraction between like molecules

• water molecules stick to each other

Adhesion

• attraction between unlike molecules

• water molecules stick to walls of xylem

Source

• where sugars are produced

• higher concentration of sugars

Sink

• where sugars are stored or used

• lower concentration of sugars

Sieve Tube Elements

• living cell without nuclei and ribosomes

• has a sieve plate

Sieve Plate

• has perforations for sugars to pass through

Companion Cells

• has nuclei and ribosomes

• supports sieve tube elements

Translocation

• the long distance transport of substances through the phloem

Radicle

• embryonic root, absorbs water for the seedling

• becomes the roots

Hypocotyl

• embryonic stem, becomes the lower stem

• between the roots and the cotyledons

• elongates and supports the cotyledons

Epicotyl

• embryonic stem, becomes the upper stem and forms mature leaves

• above cotyledons, below the plumule

• elongates and supports the first true leaves to increase sun exposure

• a stem tissue - does not perform photosynthesis

Plumule

• forms the first true leaves and shoot tip

• performs photosynthesis

Cotyledon

• first leaves of a seedling

• provides nutrients to the plant embryo

Seed Coat

• protects the embryo from external dangers (physical damage, pathogens, etc.)

• breaks open to allow the plant embryo to grow

Succession

• gradual change over time in the species that form a community

Primary Succession

• succession in a place without plants, animals, or soil

• mostly from rock or mineral deposits

Pioneer Species

• first species to colonize an area during succession

Secondary Succession

• succession in a disturbed ecosystem

• has soil

Grafting

• cutting a young branch and attaching it to the stem of another plant

Scion

• a detached young branch

Stock

• the plant which the scion is grafted

Tropism

• directional change of a growing plant in response to an external stimulus

Phototropism

• directional change of a growing plant in response to light

Gravitropism

• a directional change of a growing plant in response to gravity

Thigmotropism

• a directional change of a growing plant in response to contact

Auxins

• found in shoot apical meristems

• promotes cell elongation

Gibberellins

• found in young tissues of shoots and in developing seeds

• promotes cell division and elongation → increases height

• promotes flowering and fruit growth

Cytokinins

• found in meristems, young leaves, and growing seeds

• promotes cell division

• auxins + cytokinins → development of roots and shoots

• delays senescence (i.e. slows cell aging)

Senescence

• the process of deteriorating with age

Ethylene

• a gas, produced in all plant parts

• induces change to adapt to environmental stress

• slows down leaf and fruit senescence

• regulates growth of roots and shoots around obstacles

• promotes fruit ripening