Plant Structures Plant Structures

Plant cell structure (Review) Differences between plant & animal cells? Unlike animal cells, plant cells have... Unlike animal cells, plant cells have...chloroplasts. a central vacuole. a cell wall of cellulose (angular cells not rounded).

Plant taxonomy (Review) Of ~19 plant phyla, only 4 are wide- spread. Know a dichot- omous key to separate the plant phyla.

Plant structure (Dicotyledonous angiosperms) Shoot Above- ground Root Below- ground Note the ring of vascular tissue.

Plant tissues Plants consist of 4 types of tissue. Dermal tissue – epidermal cells, often covered with a waxy layer called the cuticle. Vascular tissue – xylem and phloem cells transport water and nutrients throughout the plant. Ground tissue – parenchyma cells lying between dermal and vascular tissue provide support with thickened cell walls. Meristematic tissue – undifferentiated cells that produce all others by mitosis.

Plant tissues Plants consist of 4 types of tissue. Dermal tissue Vascular tissue = xylem & phloem = xylem & phloem Ground tissue Meristematic tissue creates new cells creates new cells Meristem

Plant meristems Dicotyledonous plants have apical and lateral meri- stems that give birth to new cells. Apical = at tips. Lateral = at side.

Plant meristems Growth due to apical and lateral meristems Apical meristems increase plant length. Undifferentiated cells in shoot and root. bud Buds will also develop their own apical meristems

Plant meristems Growth due to apical and lateral meristems Growth due to apical and lateral meristems Lateral meristems increase plant girth. Vascular cambium makes xylem and phloem. Cork cambium makes bark (constantly replaced). Vascular cambium

Diagram of a dicot plant stem Stems hold leaves toward light & transport nutrients from roots. As the dicot plant ages, the vascular tissues form a ring. vascular tissues form a ring. Young Older

Diagram of a dicot plant stem As the dicot plant ages, meristematic cells form a ring called vascular cambium. Be able to draw this. (functions of tissues later) Be able to draw this. (functions of tissues later) The vascular cambium gives rise to the xylem & phloem tissues. Vascular cambium

Diagram of a dicot plant stem A new ring of xylem and phloem forms each year in perennial plants like trees. Xylem rings are useful for telling the age of a tree.

Monocot vs. dicot plant stem Recall that monocot stems (like corn & palms) have their vascular tissues in scattered bundles, not in rings (as do dicots like oak trees).

Transport within stems Water moves from root to leaf as sap through xylem tissue that is composed of non- living tubular cells. Xylem vessels have lateral pits and perforations at top & btm. Diameter of xylem vessel = 50 to 100 μm

Transport within stems Water moves by transpirational pull aided by cohesion, adhesion, & evaporation. Evaporation removes water from the leaf surface as a result of the lower humidity in the air compared to the leaf.

Transport wihin stems Water has polarity ( the effect of having dis- tinct ends, or poles, like a magnet ); water has opposite charges on opposite ends of the molecule. One pulls another.

Transport within stems Water moves by transpirational pull aided by cohesion, adhesion, & evaporation. Cohesion is the attractive force that one water molecule has for another (due to hydrogen bonding). Cohesion lets the insect walk on water. Water is pulled up the xylemvessels. Water is pulled up the xylemvessels.

Transport within stems Water moves by transpirational pull aided by cohesion, adhesion, & evaporation. Adhesion is the attractive force that one water molecule has for another substance – such as hydrophilic cellulose – (also due to hydrogen bonding). Xylem walls are cellulose and adhere water. Water is pulled up. pulled up.

Transport within stems So, transpirational pull is the movement of water up a plant against gravity aided by attractive forces on water molecules and resulting from evap- oration of water va- por from the leaves and stems. The tallest trees, Coast Redwoods in northern Cali- fornia, (Sequoia sempervirens), can be nearly 380’ tall).

Transport within stems Phloem is a vascular tissue that moves sap from sugar sources to sugar sinks. Phloem sap contains sucrose & amino acids. Sources (where the sugar is made) include photosynthetic tissues and storage organs. Sinks (where the sugar is need- ed) include the fruits, seeds, & roots.

Transport within stems Phloem is made of living cells called sieve tube members and companion cells. (Recall: xylem cells are dead.) (Recall: xylem cells are dead.) Sieve tube mem- bers are stack- ed to form tubes. Companion cells lie along each sieve tube mem- ber & help load sugar into the sieve tube.

Transport within stems Active translocation of sugars from source to sink in phloem. 1) Sugars are actively transported from source cells into sieve tube elements, source cells into sieve tube elements, so cells must be alive. so cells must be alive. 2) Because of the high sugar concen- tration in the phloem, water dif- tration in the phloem, water dif- fuses into the sieve tube elements, fuses into the sieve tube elements, raising the water pressure. raising the water pressure. 3) Pressure causes the sap – sugar water – to flow through the phloem. water – to flow through the phloem. 4) Sugars are transported out of the phloem into sink cells; water dif- phloem into sink cells; water dif- fuses into the xylem, reducing the fuses into the xylem, reducing the water pressure in the phloem. water pressure in the phloem.

Transport within stems Active translocation of nutrients from source to sink.

Transport within stems Review: water flows in a plant due to differences in water potential (% H 2 O). Positive pressure pushes, as in the phloem. Negative pressure pulls, as in the xylem.

Plant Structures Plant Structures

Plant structure (Dicotyledonous angiosperms) Shoot Above- ground Root Below- ground Note the ring of vascular tissue.

Plant roots Plant roots anchor plants in the ground and absorb water and dissolved minerals from the soil.

Uptake by roots Roots provide a large area for uptake of water and nutrients. Thousands of root hairs on each root.Thousands of root hairs on each root. Dozens of lateral roots.Dozens of lateral roots. Mycorrhizae (mutualistic fungi) grow out into soil.Mycorrhizae (mutualistic fungi) grow out into soil. Root hairs

Uptake by roots How do minerals reach the roots? Mass flow of the water in the soil. The roots intercept ions as they pass by.

Transport within roots Mineral ions are absorbed from the soil into roots passively & by active transport. Apoplast – non-living route of transport through cell walls to xylem. Symplast – transport route through the living cytoplasm to the xylem. Absorption can create so much root pressure that water can be forced out of leaves on humid nights.

Transport within roots Apoplastic movement (passive): Hydrophilic cellulose in the cell walls of the epidermis (root hairs are epidermal cells) absorb water & the minerals dissolved in it. Minerals & water move from one cell wall to another toward the xylem, but the Casparian strip forces a detour into the cytoplasm. (water insoluble material blocks flow through cell wall.)

Transport within roots Symplastic movement: Once within a cell’s cytoplasm, minerals move to adjacent cells by diffusion, passing from one cell to another through plasmodes- mata – tunnels in the cell walls – moving toward the xylem.

Types of edible plant roots Roots store energy; some are food sources. sweet potato

Variety of plant leaves Venus fly trap Pitcher plant Cactus (leaves are the needles) Specialized leaves

Diagram of a dicot plant leaf Leaves photosynthesize, making food for the plant. Be able to draw this.

Functions of leaf tissues Cuticle: waxy covering to prevent loss of moisture Epidermis: layer of protective cells (no chloro- plasts)

Functions of leaf tissues Mesophyll: 2 layers, both contain chloroplasts for photosynthesis Spongy parenchyma: air spaces for gas exchange

Functions of leaf tissues Vascular tissue: xylem moves water from roots; phloem moves photosynthate away from the leaf.

Functions of leaf tissues Stoma (pl. stomata): an opening in the epider- mis through which H 2 O, O 2 and CO 2 may pass. Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.

Functions of leaf tissues Stoma (pl. stomata): an opening in the epider- mis through which H 2 O, O 2 and CO 2 may pass. Guard cells: regulate gas exchange by expanding and contracting using ion pumps and osmosis to open and close the stoma.

Dicot flower structure Draw and label all: Male parts Stamen Holds pollen Female parts Carpel (= pistil) OvulationFertilization

Pollination Pollination – placement of pollen onto the stigma of a carpel (pistil) by wind or animal carriers. Pollen is a haploid (1n) spore that carries the genes of the male plant.

Pollination Pollination – placement of pollen onto the stigma of a carpel (pistil) by wind or animal carriers.

Fertilization Fertilization – union of haploid gametes to produce a diploid zygote. After the pollen germinates on the stigma, the pollen tube must grow down the style to deliver the sperm to the egg. Female Gametophyte 1n Sporophyte tissue 2n Sporophyte tissue 2n

Seed dispersal Seed dispersal – Process of moving seeds away from the parent plant. Adaptations for: Wind (feathery) Water (flotation) Animal (barbs, food source (fruit, nut)

Seed dispersal Seed dispersal – Process of moving seeds away from the parent plant.

Seed dispersal Why disperse seeds? Colonize new areas Get away from the parent plant: Excess shade Few nutrients Plant toxins

Control of plant growth Plants are rooted in the ground, yet they can still move. They bend one way or the other. Geotropism – movement due to gravity Phototropism – movement due to light Positive Phototropism Negative Geotropism

Control of plant growth Phototropism results from stimulation of plant cells by the hormone auxin. Hormones are made in one place but act elsewhere. Hormones are made in one place but act elsewhere. Auxin is made in shoot meristems. It stimulates growth (elongation) of cells. Cells on the shaded side grow larger, causing a bending of the plant shoot. Cells on the shaded side grow larger, causing a bending of the plant shoot.

Control of plant growth Phototropism results from stimulation of plant cells by the hormone auxin. Auxin, made in shoot meristems, causes cells on the dark side to elongate by loosening their cell walls; internal water pressure causes cells to expand.

Giuseppe Arcimboldo’s painting, Vertumnus Giuseppe Arcimboldo’s painting, Vertumnus