Botany

110 flashcards by MentisLibrary

The science of plants: tissues and meristems, root, stem and leaf anatomy, photosynthesis and respiration, water and sugar transport, flowers, seeds and pollination, plant hormones, and the major plant families.

What are the three tissue systems present in every plant organ?

Dermal tissue covering the surface, vascular tissue conducting water and sugars, and ground tissue filling the rest and doing most storage, support and photosynthesis.

What is a meristem?

A region of undifferentiated cells that keep dividing, providing all new cells for growth.

How do apical and lateral meristems differ?

Apical meristems sit at root and shoot tips and lengthen the plant. Lateral meristems form cylinders along the stem and root and thicken it.

Primary growth versus secondary growth

Primary growth is elongation from apical meristems and produces the primary plant body. Secondary growth is thickening from the vascular cambium and cork cambium and produces wood and bark.

What does the vascular cambium produce?

A thin cylinder of dividing cells that makes secondary xylem, which is wood, to its inside and secondary phloem to its outside.

What does the cork cambium produce and what is periderm?

The cork cambium makes cork to the outside, whose suberized walls waterproof and protect the stem. Cork plus cork cambium plus the layer beneath is the periderm, which replaces the epidermis in woody stems.

What are lenticels?

Loose, spongy patches in the periderm that let gases diffuse between the living stem tissue and the air.

What does xylem do and what is unusual about its conducting cells?

Xylem carries water and dissolved minerals upward from the roots. Its conducting cells, tracheids and vessel elements, are dead and empty at maturity, leaving hollow lignified tubes.

How do tracheids differ from vessel elements?

Tracheids are long, narrow and tapered, and water passes between them through pits. Vessel elements are wider and shorter, and their end walls are perforated so they stack into open vessels.

What does phloem do and which cells do it?

Phloem carries sugars and other organic products from sources to sinks. Sieve tube elements conduct, and they are alive but lack nuclei and most organelles, so each is kept alive by an adjacent companion cell.

Why does girdling a tree kill it?

Removing a ring of bark severs the phloem, so sugars can no longer reach the roots. The roots starve, and the whole tree dies once their reserves run out.

Compare parenchyma, collenchyma and sclerenchyma.

Parenchyma cells are alive with thin walls and do metabolism and storage. Collenchyma cells are alive with unevenly thickened primary walls and support growing parts flexibly. Sclerenchyma cells have thick lignified walls, are usually dead at maturity, and give rigid support.

What is the difference between fibers and sclereids?

Both are sclerenchyma. Fibers are long and slender and occur in strands. Sclereids are short and irregular and occur singly or in small clusters.

What does the cuticle do and where is it?

A waxy layer of cutin secreted over the outer wall of the epidermis. It blocks water loss and resists pathogen entry.

How do guard cells open and close a stoma?

Guard cells actively pump potassium ions in, water follows by osmosis, and the swollen cells bow apart because their inner walls are thicker, opening the pore. Losing the ions reverses it.

What are trichomes and what do they do?

Hairlike outgrowths of the epidermis. They reduce water loss and heat load, deter insects, and in some species hold irritating or toxic chemicals.

Why do root hairs matter so much for a plant's water supply?

Each is a thin extension of a single epidermal cell, and collectively they multiply the root surface in contact with soil water many times over.

What does the root cap do?

It is a thimble of cells over the root tip that protects the meristem as it pushes through soil, secretes lubricating mucilage, and senses gravity.

Name the zones behind a root tip in order.

The zone of cell division containing the apical meristem, then the zone of elongation where cells lengthen and push the tip forward, then the zone of maturation where cells differentiate and root hairs appear.

What is the endodermis and what does the Casparian strip do?

The endodermis is a single cell layer wrapping the root vascular cylinder. The Casparian strip is a suberin band sealing the radial walls, forcing all water and minerals to cross a plasma membrane before entering the xylem.

Where do lateral roots originate and why is that unusual?

In the pericycle, a layer just inside the endodermis, so a lateral root grows outward through the cortex and epidermis of the parent root.

Taproot system versus fibrous root system

A taproot is one dominant vertical root with smaller branches, reaching deep water. A fibrous system is a dense mat of similar-sized roots near the surface.

Define node, internode, axillary bud and terminal bud.

A node is where a leaf attaches, an internode is the stem between nodes, an axillary bud sits in the angle above a leaf and can become a branch or flower, and the terminal bud caps the shoot tip.

What is apical dominance?

Suppression of axillary buds by the growing shoot tip, largely mediated by auxin moving down from the terminal bud.

Name the parts of a typical leaf.

The blade is the flat photosynthetic surface, the petiole is the stalk attaching it to the stem, and veins carry the vascular bundles through the blade.

How do palisade and spongy mesophyll differ?

Palisade mesophyll is a layer of tightly packed columnar cells just under the upper epidermis, densely filled with chloroplasts. Spongy mesophyll below is loosely packed with large air spaces for gas diffusion.

How do you tell a simple leaf from a compound leaf?

Look for the axillary bud. A simple leaf has one blade with a bud at the base of its petiole. A compound leaf is divided into leaflets that have no bud where they attach.

What does leaf venation usually tell you about a plant's group?

Parallel venation, with major veins running the length of the blade, is typical of monocots. Netted or reticulate venation, with veins branching into a mesh, is typical of eudicots.

List the main differences between monocots and eudicots.

Monocots have one cotyledon, parallel veins, scattered vascular bundles, fibrous roots, floral parts in threes, and pollen with one aperture. Eudicots have two cotyledons, netted veins, bundles in a ring, often a taproot, parts in fours or fives, and pollen with three apertures.

What are annual rings and what makes them visible?

Each year's secondary xylem forms a ring. Earlywood grown in spring has wide thin-walled cells and looks pale; latewood grown later has narrow thick-walled cells and looks dark, so the boundary is sharp.