Ch. 35 Plant Structure, Growth, & Development

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info on plant structure from Campbell's Biology textbook, ninth edition

Tissue

group of cells consisting of 1 or more cell types
- together perform a specialized function

Organ

-several types of tissues together that carry out particular functions

3 Basic Plant Organs

leaves, stems, roots

Vegetative Growth

production of non-reproductive leaves, stems and roots

Root

organ that anchors the vascular plant in the soil
- absorbs minerals and water
- stores carbohydrates

Taproot

- one main vertical root
- develops from an embryonic root
- gives rise to lateral roots

Lateral roots

-a.k.a branch roots

adventitious roots

- grow in an unusual location such as roots arising from stems or leaves
- occurs in many monocots

fibrous root system

a mat of general thin roots spreading out below the soil surface
- do not penetrate deeply, best adapted to areas of light rainfall or shallow soils

Root hairs

- on root tips
- increase the surface area of the root enormously
- main fxn: absorption

Specialized root adaptations

Prop roots, storage roots, buttress roots, "strangling" aerial roots, & pneumatophores

Prop roots

-support the tall top-heavy trees in sandy soils

Storage roots

store food (starch) and water in their roots

Buttress roots

give architectural support to the trunks of trees in the tropics

"Strangling" aerial roots

- the strangler fig germinates in the branches of the tall trees
- they send snakelike roots that wrap around the host trees
- the host tree eventually dies from shading of the fig leaves

Pneumatophores

-aka air roots
- Ex: mangroves
- roots project above the water line, enabling the roots to obtain oxygen, which is lacking in the watery mud

Stem

-organ that raises or separates leaves, exposing them to sunlight
- raise reproductive structures for fruit and pollen dispersal
- consists of nodes and internodes

Nodes

points at which leaves are attached

Internodes

stem segments between nodes

Axillary bud

- in the upper angle(axil) formed by each leaf an the stem
- can form a lateral shoot (a branch)

Apical bud

- aka terminal bud
- area where most of the growth of a shoot begins
- composed of developing leaves and a compact series of nodes and internodes

Apical dominance

- the inhibition of axillary buds by an apical bud
- removing the apical bud stimulates the growth of axillary buds

Modified Stem Adaptations

- Rhizomes, Bulbs, Stolons, and Tubers

Rhizomes

- a horizontal shoot that grow just below the surface
- vertical shoots emerge from axillary buds on the rhizome

Bulbs

- consist of enlarged bases of leaves that store food
- Ex: onion

Stolons

- horizontal shoots that grow along the surface
- enable a plant to reproduce asexually
Ex: strawberries

Tubers

-Ex: potatoes
- enlarged ends of stolons or rhizomes specialized for storing food

Leaf

main photosynthetic organ
- consist of a blade & petiole

Blade

-flattened photosynthetic part

Petiole

- the stalk
- joins the leaf to the stem at a node
- grasses & many monocots lack these

Veins

vascular tissue of leaves
- monocots - parallel veins
-eudicots- branching network of veins

Simple Leaf

single undivided blade
- some can be deeply lobed

Compound leaf

blade consists of multiple leaflets
- a leaflet has no axillary bud at its base

Doubly compound leaf

each leaflet is divided into smaller leaflets
Ex: fern

Advantage of compound leaves

- withstands strong wind with less tearing
- can confine some pathogens

Leaf Adaptations

tendrils, spines, storage leaves, reproductive leaves, and bracts

Tendrils

forms a coil that brings the plant closer to a support structure

Spines

- on cacti - provide some shading and protection

Storage Leaves

succulents- storage water in their leaves

Reproductive leaves

some succulents produce adventitious plantlets which fall off the leaf and take root in the soil

Bracts

ex: Poinsettia
- brightly colored leaves that attract pollinators
- often mistaken for petals

Dermal Tissue System

plant's outer protective covering
-consists of epidermis, cuticle, and periderm
- 1st line of defense against of pathogens and physical damage

Epidermis

- layer of tightly packed cells in nonwoody plants

Cuticle

waxy coating on the epidermal surface
- helps prevent water loss
- in leaves and most stems

Periderm

- in woody plants, it replaces the epidermis in older regions of stems and roots

Trichomes

hairlike outgrowths of the shoot epidermis
- reduce water loss and reflect excess light
- major fxn: provide defense against insects by secreting sticky fluids to stop insects from eating them

Vascular tissue system

- consists of xylem and phloem
- carries out long distance transport of materials between roots and shoots

Xylem

- conducts water and minerals up from roots to shoots

Phloem

- transports sugars from where they are made to where they are needed

Stele

- the vascular tissue of a root or stem

Ground Tissue system

- neither part of the dermal or vascular tissue
- two types: pith and cortex

Pith

ground tissue that is internal to the vascular tissue

Cortex

ground tissue that is external to the vascular tissue

Plant Cell Types

Parenchyma, Collenchyma, Sclerenchyma, Xylem and Phloem

Parenchyma Cells

- mature cells have primary walls, most lack secondary walls
- large central vacuole
- perform most metabollic fxns of the plant
- photosynthesis occurs in chloroplast of parenchyma cells
- fleshy fruits composed of these cells
- store starch in roots and stems
- can grow an entire plant from one of these cells

Collenchyma Cells

- support younger parts of the plant shoot
- elongated and have thicker primary walls
- ex: the strings of celery
- provide flexible support w/o restraining growth
- living at maturity

Sclerenchyma Cells

- fxn in support
- more rigid than collenchyma cells - contain lignin
- dead at maturity- cannot elongate
2 types of these cells: sclereids and fibers

Sclereids

- boxier than fibers & irregular shape
- used for support and strengthening
- very thick secondary walls
- give nut shells their hardness

Fibers

long, slender and tapered
- used to make linens
fxn: strength and support

Xylem

- transports minerals and water
- two types of cells : tracheids & vessel elements

Tracheids

- long, thin and tapered
- water moves through pits, so it doesn't have to cross the thick secondary walls
- dead at maturity
- all vascular plants have these
- walls have lignin

Vessel Elements

- wider and shorter than tracheids
- lignified walls & dead at maturity
- found mainly in angiosperms
- aligned end to end forming miropipes called vessels, with the end walls having perforation plates that enable water to flow freely between them

Phloem

-moves sugar throughout the plant
- alive at maturity
- 2 types of cells: sieve tube elements and companion cells

Sieve Tube Elements

- transports nutrients in chain of sieve tubes
- lack a nucleus, ribosomes, vacuole, and cytoskeletal elements --> allows nutrients to pass more easily
- end walls of the sieve tubes are seperated by the sieve plates that have pores to facilitate flow through the sieve tubes

Companion cells

- non- conducting cell found along side the sieve tube elements
- connected via plasmodesmata
- help load sugars into the sieve tube elements

Indeterminate Growth

- process of growth that continues all throughout a plant's life

Meristems

areas of undifferentiated growth that divide and lead to new cells that elongate
- 2 types: apical and lateral meristems

Apical meristems

- located at the tips of roots and shoots and in axillary buds of shoots
- provide additional cells that enable growth in length

primary growth

growth in length in the vertical direction
- allows roots to extend in the soil and shoots to increase their exposure to light

Secondary growth

growth in thickness
- caused by lateral meristems
- occurs in roots and woody stems
- rarely seen in monocots

Lateral meristems

- called vascular and cork cambiums

Vascular cambium

adds layers of vascular tissue called the secondary xylem and phloem

Cork cambium

replaces the epidermis with thicker periderm
- adds secondary dermal tissue

Annuals

- complete life cycle( germination to flowering to seed production to death) in a year or less

Biennials

- require two growing seasons to complete thier life cycle, flowering only in the second year

Perennials

- live many years and include trees, shrubs, and grasses

Root cap

- covers the root tip
- protects the apical meristem as the root pushes through the soil
- secretes polysaccharide slime to lubricate soil around the root tip

Zones of Growth in a Root

Zones of Cell division, elongation, and maturation (differentiation)

Zone of Cell Division

- includes the root apical meristem
- new root cells are produced here

Zone of Elongation

- most of the growth occurs here
- cells elongate, pushing the root tip further into the soil

Zone of Differentiation

- cells complete their formation into specialized functioning cells and become distinct cell types

Root Cross section of a Eudicot

- vascular tissue(xylem and phloem) is in the center in the shape of an "X"

Root Cross section of a Monocot

- vascular tissue is in the center but more spread out in a circle with a core of parenchyma cells in the very center

Endodermis

-innermost layer of the cortex
- surrounds the vascular cylinder
- regulates passage of substances from the soil into the vascular tissue

Pericycle

- where lateral roots grow from
- outermost cell layer in the vascular cylinder
- a ring just inside the endodermis

Leaf primordia

-finger like projections on either side of the apical meristem in a shoot tip

Branching

- part of shoot primary growth
- arises from the activation of axillary buds
- the closer the axillary bud is to an active apical bud, the more inhibited it is

Lateral shoots

- develop from axillary bud meristems on the stem's surface and disrupt no other tissues

Cross section of a Eudicot stem

- vascular tissue is arranged in a ring
- xylem is on the inside and phloem on the outside

Cross section of a Monocot stem

vascular bundles are all scattered throughout the stem
- don't graph well
- look like a monkey face

Stomata

- located on the epidermis of leaves
- allow gas exchange (CO2 and O2) between leaf and air
- major avenue for evaporative water loss
- surrounded by 2 guard cells

Guard Cell

- regulate the opening and closing of the stomata pore

Mesophyll

ground tissue of a leaf
- in between the upper and lower epidermis layers
2 layers: palisade and spongy mesophyll

Palisade mesophyll

- has parenchyma cells specialized for photosynthesis
- upper layer of mesophyll

Spongy mesophyll

- parenchyma cells are arranged loosely with air spaces so that oxygen can circulate around

Bundle sheath

- parenchyma cells that surround the vein of vascular tissue in a plant leaf

Vascular cambium

- adds layers of secondary xylem to its interior and secondary phloem to its exterior--> thickens roots and stems
- the layers of xylem (wood) accumulates over the years = tree rings
-older secondary xylem usually gets sloughed off-does not accumulate like the xylem in a tree

Vascular rays

- radial files of parenchyma cells that connect the secondary xylem and phloem
-fxn: aid in wound repair, store carbs, and move water and nutrients between the xylem & phloem

Bark

- everything exterior to the vascular cambium
- secondary xylem, cork, cork cambium

Periderm

cork and the cork cambium

Heartwood

- layers of secondary xylem that no longer transports water and minerals
- closer to the center of a stem or root
- darker colored than sapwood

Sapwood

- newest, outer layers of secondary xylem that still transport water and minerals

Asymmetrical cell division

- one daughter cell receives more cytoplasm than the other during mitosis
- how guard cells form around the stomata

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