Plant biology unit 3

Root function

Anchor plant in soil, absorb and conduct water and minerals, produces hormones, food storage

Where to find taproots

Dicots and gymnosperms

Taproot

Large main root developed directly from the radicle. Produces branch roots. Penetrates deep in the soil and spread out

Where to find fibrous roots

Seedless vascular plants, monocots

Fibrous roots

Radicle dies and numerous roots grow from lower part of stem. Adventitious roots, each one develops lateral roots. Shallower, more spreading

3 root zones

zone of cell division, zone of elongation, zone of maturation

Zone of cell division

apical meristem at root tip. Subdivided into protoderm, ground meristem, procambium

Root cap

Produced by root apical meristem, protects root, produces mucigel

Stele

Central cylinder of vascular and ground surrounded by cortex

Protostele

simplest type of stele

Pericycle

encircles stele, made of meristematic cells that give rise to lateral roots

Endodermis

regulates flow of materials between cortex and vascular tissues, surrounded on 4 of its 6 sides by casparian strips

Casparian strips

Specialized bands of suberin found in the endodermis of plant roots. They act as a barrier, preventing the movement of water and solutes between cells.

Aerial roots

Adventitious roots arise from stems, extra support

Buttress roots

flared roots that extend from tree trunks, stabilizes tree

Contractile roots

Shorten and pull plant deeper into soil

Suckers

Asexual reproduction, arise from underground roots, comes through soil

Pneumatophores

Air roots, provide oxygen for plants in swampy areas

Haustoria roots

parasitic roots, penetrates stems and roots of other plant to get nutrients

Endomychorrhizae

fungi penetrate plant roots, produces branching called arbuscules

Ectomychorrhizae

Network of fungi surrounds roots, produces mantle sheath

Nitrogen fixing bacteria

convert nitrogen into ammonium. Plants then take up fixed nitrogen, bacteria will infect roots, the roots form nodules for bacteria t0 live in which releases nitrates into soil

Zone of elongation

derivatives stop dividing and begin elongating

Zone of maturation

cells differentiate, roots hairs formed by epidermal cells

Guard cells

Specialized cells found in the epidermis of plant leaves that control the opening and closing of stomata.

Suberin

A waxy substance found in the cell walls of plants, especially in cork. It provides waterproofing and protection against pathogens and pests.

Corms

Resemble bulbs, made of stem tissue with papery leaves, stores food. Crocus

Rhizomes

Horizontal stems that grow below ground and have long-short internodes. Irises

Stolons

Horiztonal stems grow above ground and have long internodes

Tubers

swollen fleshy underground stem, stores food

Bulbs

Large buds surrounded by fleshy leaves with a small stem at lower end, stores food. Onions, tulips

Cotyledons

Seed leaves, stores good for germinating seed

Radicle

embryonic root

Plumule

embryonic shoot, generates epicotyl

Hypocotyl

portion of the embryonic stem under the cotyledon and above radicle

Endosperm

Food storage tissue surrounding the embryo, breaks down to nourish embryo

Testa

seed coat

Leaf epidermis

Single layer of non photosynthetic cells derived from protoderm. Prevents water loss, abrasions, entry of diseases. Regulates gas exchange through stomates. Transpiration pulls water and minerals up roots and cools the leaf

Netted venation

Branching networks, most dicots and ferns

Parallel venation

long lines, most monocots and gymnosperms

Thorns

Sharp, pointed, and protective structures found on the stems or branches of certain plants. Thorns deter animals from feeding on the plant, acting as a defense mechanism.

Bracts

Modified leaves found at the base of a flower or flower cluster. They are often brightly colored and attract pollinators.

Lateral meristems

Type of meristem responsible for the growth in girth of plants. Found in the cambium layer. Produces secondary tissues such as secondary xylem and phloem.

2 types of lateral meristems

Vascular cambium and cork cambium

Where are lateral meristems?

Woody plants

What do lateral meristems produce?

Secondary growth

Wood vs bark

Bark is thinner, wood is secondary xylem

Lenticels

Small openings in the bark of woody plants that allow for gas exchange between the internal tissues and the external environment.

Vascular cambium

secondary xylem and phloem

Cork cambium

produces periderm, does not expand in diameter, new cambium forms within old cork cambium

Inflorescence

A compact cluster of flowers on a plant stem, often surrounded by modified leaves.

Examples of modified leaves

thorns, tendrils, bracts

Examples of modified roots

Aerial roots, buttress roots

Example of modified stems

Rhizomes, stolons, tubers, bulbs

Pericycle

Outermost layer of the vascular cylinder in plants, located just inside the endodermis. It gives rise to lateral roots and secondary growth.

Stem anatomy

leaves attach at internodes, nodes, dormant axillary buds

Lignin

A complex polymer found in plant cell walls that provides structural support and rigidity. It is the second most abundant organic compound on Earth, after cellulose. Lignin is responsible for the woody texture of plants and is highly resistant to degradation, making it difficult to break down in industrial processes.

Mucigel

Substance secreted by root cells that lubricates and protects the root surface. It helps plants absorb water and nutrients efficiently.

Palisade mesophyll

elongated thick layer lined up under upper epidermis

Spongy mesophyll

loosely organized layer that has space for diffusion for CO2 to travel from stomata to other parts of a leaf

Abscission zones

Specialized regions in plants where leaves, flowers, or fruits detach from the plant. They contain cells that weaken and break down the connection between the plant and the organ, allowing for its separation. triggered by environment

Rays

divide to produce parenchyma cells for storage

Fruit anatomy

Pericarp: exocarp, mesocarp, endocarp

Seed

Fruit

protect embryo from drying out, promote seed distribution, consists of one or more mature ovaries

Quiescent center

A region of undifferentiated cells located in the root meristem of plants. It plays a crucial role in maintaining the stem cell population and is responsible for the regeneration of damaged tissues.

Adventitious roots

Roots that develop from non-root tissues, such as stems or leaves. They help plants anchor in soil, absorb water and nutrients, and provide additional support. Adventitious roots are commonly found in plants like ivy, corn, and mangroves.

Intercalary meristems

Sphionostele

most seedless vascular plants. Continuous cylinder that surrounds a core of pith

Eustele

most gymnosperms and dicots. Forms vascular bundles of xylem and phloem. Vascular bundles arranged in a circle around the pith

2 models of shoot apical meristem

Zone model and cell layer model

Zone model

shoot apical meristem has 3 regions.

Central mother cell zone: divides and makes cells of peripheral and pith zones

Peripheral zone: divides to make leaf primordia and cells for protoderm, procambium, and ground meristem

Pith zone: Divides to make cells for ground meristem

Cell Layer Model

initials of shoot apical meristem form several cell layers. Outer layers are tunica, creates protoderm. Inner layer is corpus, created procambium and ground meristem

Periderm

produced by cork cambium, produces cork

Hardwood vs sapwood

Hardwood: Many fibers, burns longer, harder to damage, denser, dicot trees

Sapwood: Less fibers, burns fast, softer, less dense, conifers

Reaction wood vs tension wood

Reaction wood: Irregular growth pattern due to wind or gravity

Tension wood: Response to bending

Monocot vascular bundles

scattered throughout ground tissue

Dicot vascular bundles

arranged in a ring

Growth rings

Forms from vascular cambium annually

Meiosis vs mitosis

Mitosis: independent homologous chromosome, identical daughter cells

Meiosis: homologous chromosomes pair forming bivalents until anaphase 1, chromosome number reduces, daughter cells are haploid, daughter cells have new assortment of parental chromosomes

Meiosis 1

S phase

Prophase 1

Metaphase 1

Anaphase 1

Telophase 1

Cytokinesis

Meiosis S phase

chromosomes replicated

Prophase 1

homologous chromosomes form pairs, a tetrad of 4 chromatids

Metaphase 1

Tetrads move onto metaphase plate

Anaphase 1

phase when overall chromosome numbers is halved for each of the 2 new daughter cells

Telophase 1

Cell returns to pre-meiotic state

Meiosis II

similar to mitosis, begins with haploid cells, ends with 4 haploid nuclei. Daughter cells become spores

Haploid

Has 1 set of chromosomes

Diploid

Has 2 set of chromosomes

Asexual reproduction

Involves 1 parent, mitosis

Produces genetically identical offspring (clones), rapid and effective allowing spread of an organism, no diversity

Sexual reproduction

Forms new individual by combining 2 haploid cells (gametes), takes a lot of energy but gives genetic advantage

Alternation of generations

the two adult forms alternate in producing each other

Sporophyte

consists of diploid cells

Gametophyte

consists of haploid cells

Gametes

sperm and egg

Double fertilization

the fusion of the egg and sperm and the simultaneous fusion of a second sperm and two polar nuclei that ultimately results in the formation of the endosperm (the food-storage tissue) of the seed.

Gymnosperm pollination

different cones on same plant participate in pollination

Angiosperm pollination

different parts of same flower participate in pollination if perfect flower

Imperfect flower pollination

Monoecious: Male and female flowers on same plant pollinate

Dioecious: Male or female flowers on different plants pollinate

Complete flower

contains sepals, petals, stamens, carpels

Incomplete flower

missing 1 or more parts