Seed Plant Structure & Function ch 31 All

Materials © Cmassengale

Seed Plant Overview:

The plant body consists of two basic parts--- the shoot system and the root system

Shoot system is above ground and includes organs such as leaves, buds, stems, flowers, and fruits

The functions of the shoot system include photosynthesis, reproduction, storage, transport, and hormone production

The root system is below ground and includes roots as well as modified stem structures such as tubers and rhizomes

The functions of the root system include anchorage, absorption, storage, transport, and production of certain hormones

Seed plants contain 2 types of vascular tissue (xylem & phloem) to help transport water, minerals, & food throughout the root & shoot systems

Plant cells have several specialized structures including a central vacuole for storage, plastids for storage of pigments, and a thick cell wall of cellulose

Plant cells are all box-shaped in appearance

Plant cells are arranged into tissues and tissue systems A simple tissue is composed of only one type of cell; a complex

tissue is composed of more than one cell type.

Plants are composed of specialized cells and tissues

In plants, the formation of new cells, tissues and organs is restricted almost entirely to regions known as meristems

Meristems:

There are 3 main types of meristematic tissue in vascular seed plants   ---- apical, intercalary, & lateral meristems

Apical Meristem occur at the tips of roots and shoots and are responsible for the length-wise extension of the plant body known as primary growth

Cells in apical meristems are produced by mitosis & then differentiate into specialized cells & tissues

The apical meristem gives rise to 3 primary meristems --- Protoderm (gives rise to outer covering of plant), Procambium (gives rise to vascular tissue), and Ground meristem (gives rise to the 3 types of plant cells)

Root Tip with Meristems

Some monocots, such as grasses & bamboo, have intercalary meristems located above the bases of leaves and stems  allowing them to regrow quickly after being cut down

Woody plants have meristem between xylem & phloem to produce wood

Lateral meristems produce outward growth in plants or secondary growth

Lateral meristems are called cambium (cambia, plural)

Vascular cambium makes wood & vascular tissues and cork cambium makes cork & bark

Plants without lateral meristems have only primary, not secondary growth and are called herbaceous plants

Specialized Plant Cells:

Plants have 3 basic types of cells --- parenchyma, collenchyma, & sclerenchyma

Parenchyma cells are the most abundant & least specialized

Parenchyma are loosely-packed, cube shaped or elongate cells with a large central vacuole & thin cell walls

Parenchyma Cells

Parenchyma cells can specialize for various functions (storage, photosynthesis, etc.)

Parenchyma form the bulk of non-woody plants such as the fleshy part of an apple

Collenchyma cells are irregular in shape with thicker cell walls & support the growing parts of plants

Collenchyma cells

Collenchyma cell walls are also flexible to support new growth regions of the plant (example: tough strings on a celery stalk)

Sclerenchyma cells support non-growing parts of plants because they have thick, rigid, non-stretchable cell walls

Sclerenchyma Cells

Sclerenchyma cells often die at maturity leaving empty, box-like structures 

Two types of sclerenchyma cells are fibers & sclereids  

Fibers are cells up to 50cm long that usually occur in strands such as linen & flax

Sclerenchyma Fibers

Sclereids have thicker cell walls & come in many shapes

Sclereids may be single cells or groups of cells and give pears their gritty texture & give hardness to peach pits & walnut shells

Other Plant Tissues & Systems:

Tissues are groups of cells with similar structures & functions Plants have 3 tissue systems --- ground, dermal, and vascular

tissues

Plant tissues make up the main organs of a plant --- root, stem, leaf, & flower

Ground tissue makes up most of the plant's body, dermal tissue covers the outside of the plant, & vascular tissue conducts water & nutrients

Dermal Tissue:

Covers the plant body and consists of epidermis in young plants & non-woody plants that  is replaced later by periderm in woody plant 

Epidermis is made of parenchyma cells in a single layer

Epidermis on stem and leaves prevents water loss by transpiration & produces a waxy material called cuticle

Epidermis Of a Leaf

Epidermal cells on roots form extensions called root hairs to absorb H20 & nutrients

Openings in the epidermis on the underside of a leaf where gases are exchanged are called stomata (stoma, singular)

Sausage-shaped guard cells are found on each side of the stoma to help open and close the pore to prevent water loss

Dead cork cells replace epidermis in woody stems & roots

Ground Tissue:

Ground tissue constitutes the majority of the plant body and contains parenchyma, collenchyma, and sclerenchyma cells

Ground tissue of the leaf (called mesophyll) uses the energy in sunlight to synthesize sugars in a process known as photosynthesis

Spongy Mesophyll of Leaf

Ground tissue of the stem (called pith and cortex) develops support cells to hold the young plant upright

Ground tissue of the root (also called cortex) often stores energy- rich carbohydrates

Vascular Tissue:

Vascular tissues transport water and dissolved substances inside the plant and helps support the stem

The 2 types of vascular tissue are xylem & phloem

Xylem carries water and dissolved ions from the roots to stems and leaves

Phloem carries dissolved sugars from the leaves to all other parts of the plant

Xylem has 2 kinds of conducting cells --- tracheids & vessel elements 

  Xylem Cells

Tracheids are long, narrow sclerenchyma cells with walls and pits for water to move between them  

Vessel elements are short, wide sclerenchyma cells without end walls stacked on top of each other

Angiosperms (flowering plants) have tracheids & vessel elements, while gymnosperms (cone bearers) only have tracheids

Phloem moves sap (dissolved sugars & minerals) from source (where they are made) to sink (where they will be used)

Phloem Cells

Phloem is made of cells called sieve tube members and companion cells

sieve tube members are stacked to form tubes called sieve tubes with porous sieve plates between the cells for movement of sugars

Companion cells are along each sieve tube member & help in loading sugar into the sieve tube

Root System:

Roots grow underground (subterranean part of the plant) Roots have 3 main functions --- (1)anchor plants (2) absorb and

conduct water & minerals (3) store food

Root & Shoot System of a Plant

The first root to emerge from the most seeds is called the primary root or taproot & can grow deep to reach water 

Taproots may store food (carrot & beet)

Taproot

Monocots have highly branched, roots called fibrous roots that grow near the surface & spread out to collect water

Fibrous roots such as in grasses often help prevent erosion

Fibrous Roots 

Adventitious roots grow from a stem or leaf above ground in some plants and serve to prop up or support the plant (corn)

Adventitious Roots

Aerial roots obtain water & minerals from the air & enable the plant to climb (orchids & ivy)

Aerial Roots of an Orchid

Structure of the Root:

Root cap covers the apical meristem (growth tissue) at the tip of the root & produces  a slimy substance so roots can more easily grow through the ground

Apical meristem replaces cells of the root cap as they are damaged

Root Structure

Epidermis covers the outside of the root & has extensions called root hairs that absorb water & minerals and increase the surface area of the root

Root Hairs

The core of the root is called the vascular cylinder & contains xylem & phloem

A band of ground tissue called cortex surrounds the vascular cylinder

A single cell layer called endodermis separates the cortex & vascular tissue

Endodermal cells are coated with a waxy layer called the Casparian strip so water is channeled into the vascular tissue

The Pericycle is the outermost layer central vascular tissue & forms lateral roots

Vascular tissue in dicots is at the center of the root In monocots, vascular tissue forms a ring around pith at the root

center

Secondary growth begins when the vascular cambium forms between Xylem and Phloem

Vascular Cambium produces secondary xylem toward the inside of the root and secondary phloem toward the outside

 

Root Functions:

Anchor plants Absorb water & nutrients (13 essential)

May store carbohydrates (carrots, potatoes, turnips)

May store water for dry periods

Plant Cells use minerals, such as nitrogen and potassium in LARGE amounts; called macronutrients 

Minerals needed in SMALL amounts are called micronutrients

Mineral deficiencies or excess minerals can kill plants

Stem Structure & Function:

Adapted to support leaves Transport water & minerals 

Transport sugars (usually sucrose) from Source (where they're made) to Sink (where they're stored)

Movement of sugars is called translocation

Store food and/or water

Tubers (potatoes) underground food storage stems

Stems grow from the tip or apical meristem

Stems increase in circumference by lateral meristems

Leaves are attached to stems at nodes & have lateral buds that can develop into new stems or branches

Internode is space between nodes on a stem

The tip of each stem usually has a Terminal Bud enclosed by specialized leaves called Bud Scales

Vascular Tissue is arranged in bundles with xylem toward the inside & phloem toward the outside

Vascular bundles are scattered throughout monocot stems 

Vascular bundles are arranged in rings in dicot stems 

Secondary grow (woody growth) occurs in dicots, but less often in monocots

Plants with only primary growth (non-woody) are called herbaceous

Darker wood in the center of a tree trunk is called Heartwood and is composed of old, non-functional xylem

New, functional xylem makes up lighter wood in the tree trunk and is called Sapwood

Sapwood gets wider, but heartwood remains the same size

Bark is the protective covering of Woody Plants & consists of Cork, Cork Cambium, and Phloem

Springwood forms in spring when there is lots of water & xylem cells are wide with thin walls

Summerwood forms when there is less water & smaller xylem cells with thick walls form

In a Stem Cross Section, the abrupt change between Small Summerwood Cells and the following year's Large Springwood Cells produces an ANNUAL RING

Translocation of Sugars:

Phloem cells move sugars through a plant Sugars made in photosynthetic cells are PUMPED into Sieve

Tubes by ACTIVE TRANSPORT at the Source

Turgor Pressure Increases as Water enters the Sieve Tube by Osmosis

TURGOR moves the SAP toward the SINKS

Known as the PRESSURE-FLOW HYPOTHESIS

Transport of Water:

Transport of Water and mineral Nutrients occurs in the Xylem Water movement in plants is driven by Transpiration

(evaporation of water from leaves & stems)

As water evaporates, more water is pulled into the roots

Transpiration produces a NEGATIVE pressure in the xylem pulling water UPWARD

Water molecules are cohesive (attracted to each other) which also pulls water upward

Water is also adhesive sticking to the walls of the xylem

Known as Cohesion Theory of water movement

Leaf Structure & Function:

Flat surfaces helps leaves capture sunlight for photosynthesis Convert carbon dioxide and water into simple sugars (glucose)

Some leaves store food (onion) and water

Protect (cactus spines)

Used  Dyes, Fibers, Fuels, Drugs, Wax, Soap, Spices and Food

Attached by a stem-like petiole to the plant

Simple leaves have one blade, while compound leaves have several leaflets

Covered with a single layer of cells called epidermis (upper & lower)

A waxy cuticle prevents water loss

Openings called stomata on the underside of leaves for gas exchange (CO2 & O2)

Two guard cells on either side of the stomata open & close the openings

When guard cells LOSE water, the stoma CLOSE, while the stoma OPEN when guard cells gain water & swell

Stomata are CLOSED during the HOTTEST parts of the day to prevent water loss from leaves

Below the epidermis are 2 types of chlorophyll containing MESOPHYLL cells ---palisade & spongy

PALISADE mesophyll cells are closely packed columnar cells (most photosynthesis occurs here)

SPONGY mesophyll cells are loosely packed with air spaces containing CO2 & O2

VASCULAR BUNDLES (xylem & Phloem) in the spongy mesophyll appear as VEINS on the surface of the leaf

VENATION is the arrangement of veins in a leaf Monocots leaves (such as Grasses or Corn Plants) have Parallel

Venation

Dicots leaves form a Branched network called Net Venation

MONOCOT (left)        DICOT (right)

In carnivorous plants (Venus Fly Trap), the leaves trap insects for food so the plant can get enough nitrogen (grow in N2 poor soil)