PLANT FORM AND FUNCTION

Angiosperm Structure

– Monocotyledons a.k.a. monocots (newer still)

Have a single seed leaf

- Dicotyledons and/or Eudicotyledons a.k.a. eudicots (newest)

Have double seed leaves

Palms and Bananas are Monocots

Rice, wheat, corn – all monocots

Monocots vs. Dicots

Basic Angiosperm Morphology

•Reproductive structures in order simplest to most complex- sperm, pollen, anther, flower, and plant.•Seeds-seed coat protects and keeps seed from drying out.•Fruit-protects seeds, helps with seed dispersal, and is a food source for many organisms. (do not aid in pollination).•Shoot system= stems and leaves•Root system= tap root and lateral roots

Plant Morphology•Stems consist of alternating “nodes”, the site of leaf attachment

•The angle created where the leaf attaches to the stem is called the axil

•The axil contains an axillary bud, which can give rise to a lateral shoot or a branch

•The tip of the shoot is called the apex and holds the terminal bud

•The terminal bud and the apex is where the elongation of the shoot occurs

•The apical bud inhibits the growth of the axillary buds - therefore the advent of the practice of pruning

Purpose of roots• The entire root structure

serves to anchor the plant/tree in the soil

• Absorption of water and nutrients from the soil actually occurs only at the tips of each root fiber

• Millions of tiny roots hairs in these tip areas help absorption by increasing surface area

Fibrous vs. Tap Roots

• Seedless vascular plants (ferns) and Moncot angiosperms such as grasses have fibrous roots

• Dicot angiosperm have tap roots

Adventitious Roots

Roots that grow out of the stem or trunk - sometimes for extra support, sometimes for vegetative reproduction

Other modified roots• Aerating roots (or

pneumatophores): roots rising above the ground, have a large number pores for exchange of gases.

• Buttress roots are large roots on all sides of a tall or shallowly rooted tree. Typically they are found in rainforests where soils are poor so roots don't go deep. They prevent the tree from falling over and help gather more nutrients.

More modified roots

• Storage Roots: Beets, radish, turnip, horseradish, sweet potato, and cassava (tapioca).

Types of leaves

Compound Leaves Simple Leaves

Single and double compound leaves

Modified leaves

• Spines on cacti are actually leaves. The photosynthesis is carried out by the green stems

• Bracts on poinsettias are actually not petals, but leaves around the tiny yellow flowers

Tendrils for grasping

LEAF STRUCTURE

Where mostphotosynthesis occurs.

Review of the typical Plant Cell

Major Plant CellsMajor Plant Cells• Parenchyma cellsParenchyma cells• Collenchyma cellsCollenchyma cells• Sclerenchyma cells Sclerenchyma cells

– FibersFibers– SchlereidsSchlereids

• Water-conducting cells of the XylemWater-conducting cells of the Xylem– TracheidsTracheids– Vessel elementsVessel elements

• Food-conducting cells of the PhloemFood-conducting cells of the Phloem– Sieve-tube membersSieve-tube members– Companion cellsCompanion cells

Parenchyma cells• Typical plant cell – most abundant in plants• Thin walled (Walls contain cellulose, not lignin)• Unspecialized – can either photosynthesize, or store starch

– Can be found in leaves – contain chloroplasts and carry out photosynthesis (mesophyll cells are an example)

– Can also be found in roots and other non-photosynthesizing parts and store starch in amyloplasts (related to chloroplasts) – in stems they are called the pith

amyloplasts chloroplasts

Collenchyma cells• These cells are usually just under the epidermis of leaves, stems and roots• Collenchyma cells are collectively also called the cortex• Cells are columnar in shape• Also lack lignin in their cell walls, but have thicker walls than parenchyma

cells• Give younger plants or plant parts support

Because they have thick walls but lack lignin, they are able to provide support without restricting growth – hence found in young, growing parts

Epidermis

Collenchyma

Parenchyma

Columnar Collenchyma

Sclerenchyma cells

• Thick walls that are fortified with lignin (secondary wall) making them much more rigid than collenchyma walls

• Mature sclerenchyma cells usually do not contain protoplasts and cannot grow/elongate, so these cells are located in regions of the plant that have stopped growing

Sclerenchyma cont’d.• Two types of sclerenchyma cells:

– Fibers - long and thin, exist in bundles in stems, right above above vascular tissue

– Sclereids – shorter than fibers and give nutshells and seed coats their hardness. The gritty texture of certain fruit like pears is basically due to sclereids scattered among the parenchyma tissue

Xylem Cells• Xylem conducts water and minerals

up from the roots• Elongated• Produce lignin-containing secondary

walls• Lack protoplasts after maturity• Two types:

– Tracheid cell – spindle-shape, with pits in which water passes from tracheid cell to tracheid cell.

– Vessel element cells are broader and lie end to end and form continuous hollow tubes for water to flow through

Phloem Cells

• Transports sugar down from the leaves.• Two types:

– Sieve-tube cells –conducting cells of the phloem tissue.

– Companion cells – connected to sieve-tube cells, contain nuclei and ribosomes, so help maintain sieve-tube cells

Sieve-tube elements and companion cells of the Phloem

Three Tissue System

• The cells we have learned about in the past slides such as parenchyma, sieve tube cells, etc. can be placed into 3 main tissue categories or systems:– Dermal tissue system– Vascular tissue system– Ground tissue system

Three Tissue System, cont’d.Tissue System

and Its FunctionsComponent Tissues Location of Tissue

Systems

Dermal Tissue System• protection• prevention of water loss

EpidermisPeriderm (in older stems and roots)

                             

Ground Tissue System• photosynthesis• food storage• regeneration • support• protection

Parenchyma tissue

Collenchyma tissueSclerenchyma tissue

Vascular Tissue System• transport of water and minerals• transport of food

Xylem tissue (Tracheids and vessel elements)

Phloem tissue (Sieve-tube members and companion cells)

Cross Section of a Monocot Stem

Epidermis

Collenchyma (also called the cortex – which is ground tissue between the epidermis and the vascular bundles)

Parenchyma or pith

Sclerenchyma

Xylem

Phloem

Also known as the Pith in stems – stores food (amyloplasts) and water (central vacuoles)

CROSS SECTION OF AN HERBACEOUS DICOT STEM

Vascular bundle

A thin layer of cells called the vascular cambium separates the xylem and phloem

Summary of dicot & monocot stems

(Parenchyma)

(Collenchyma)

Vascular bundles in celery

Summary of Monocot vs. Dicot Stems

Summary of monocot & dicot roots

Growth in Plants

• Animals undergo determinate growth – they stop growing after they reach a certain size.

• Plants on the other hand have indeterminate growth – they continue to grow throughout their life.

Annual, Biennials, Perennials

• Botanically, an annual plant is a plant that usually germinates, flowers and dies in one year. (Impatiens, sunflower, gerbera daisies)

• A perennial plant is a plant that lives for more than two years. Perennial plants are divided into two large groups, those that are woody and those that are Herbaceous. (Roses, sage, peonies)

• A biennial plant is a flowering plant that takes between twelve and twenty-four months to complete its lifecycle. (Parsley, foxglove, sweet William)

How can plants have constant growth?

• They can have indeterminate growth because they have perpetual embryonic tissues (like stem cells in animals)

• These embryonic tissues are called Meristems or cambiums.

Meristems• There are 2 main types of meristems (embryonic

tissues):1. Apical meristems – they are located in the

terminal and axillary buds of shoots and root tips– Parenchyma cells, collenchyma cells and sclerenchyma

cells all come from apical meristems– Herbaceous plants (non-woody) the entire plant

develops due to primary growth from apical meristems

Meristems, cont’d.2. Lateral meristems (also called Cambiums) – are also located

in shoots and roots, but are responsible for secondary growth or lateral growth – they make the stems and roots thicker by growing sideways Woody plants and trees grow in thickness in areas where primary growth has stopped.

There are 2 types of lateral meristems:a. Vascular cambiums: this produces secondary xylem and

phloems which are actually wood. The vascular cambium is the source of both the secondary xylem the secondary phloem.

b. Cork cambiums – replace the epidermis with peridermis which is bark or cork in some trees

The main component of Bark in terrestrial Plants isPhloem and cork cells

Meristems, cont’d.

Lateral growth Vertical growth

Vertical growth

Stomata

• Located on the ventral side of the leaf. • Function regulation of water loss.

Plant Movement

• Tropism-are directional movement responses that occur in response to a directional stimulus

• Phototropism – movement toward light – caused by photoreceptors on shoot tips and auxins

• Gravitropism – response to gravity (seeds always germinate in the right direction) – caused by plastids called statoliths that contain dense grains of starch, in root tips and auxins

• Thigmotropism – response to touch (ivy grasping supports), caused by ethylene

• Nastic response-plant movements that occur in response to environmental stimuli but unlike tropic movements, the direction of the response is not dependent on the direction of the stimulus. These include the closing of the carnivorous Venus Flytrap leaf when it captures prey or the folding of the mimosa leaf when it is disturbed.

http://botit.botany.wisc.edu/images/130/Tropisms/Thigmotropism_MC_.php

Photoperiodism

• When a plant responds to amount to light available - e.g. by flowering

• Controlled by proteins called phytochromes• Phytochrome is a photoreceptor, a pigment that plants

use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the – germination of seeds, – elongation of seedlings, – the size, shape and number of leaves, and – the synthesis of chlorophyll.

• Plants make several different phytochromes

EpiphytesEpiphytes

• Plants that attach to other plantsPlants that attach to other plants

• Epiphytes usually derive only physical Epiphytes usually derive only physical support and not nutrition from their host, support and not nutrition from their host, though they may sometimes damage though they may sometimes damage the host. Hence, they are NOT parasiticthe host. Hence, they are NOT parasitic

• They do this to get more light and rain They do this to get more light and rain water in a rainforest canopywater in a rainforest canopy

BromeliadBromeliad

OrchidOrchid

Parasitic Plants

• Derive all or some nutrients from host plant

• Parasitic plants have a modified root, the haustoriumhaustorium, that penetrates the host plant and connects to the xylem, phloem, or both, in stems or roots of the host plant.

• Examples: Mistletoe, Dodder, Rafflesia

Parasitic PlantsJapanese DodderJapanese Dodder MistletoeMistletoe

RafflesiaRafflesia

Carnivorous Plants

• Grow in nutrient poor soil such as bogs.• High acidity in bogs prevents growth of much-

needed nitrogen cycle bacteria• Most plants cannot grow in such soil• Carnivorous plants evolved a mechanism to trap

and digest insects• This adaptation helped them overcome the

nitrate dilemma • Examples: Pitcher plants, sundews, Venus fly-

trap

Carnivorous Plants

Pitcher Plant

Sundews

Venus Flytrap

THE ENDTHE END