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Terms

Xylem

The vascular tissue that transports water and is dead when functional.

Alternation Of Generations

The generalized life cycle of plants. Unlike humans, who are structurally pretty much the same from one generation to the next, plants alternate lifestyles between generations. A haploid, gametophyte generation is followed by a diploid, sporophyte generation, which gives rise to another haploid, sporophyte generation. Alternation of generations originated in algae (which aren’t plants, for the record), but in most land plants, the sporophyte and gametophyte generation look completely different from each other.

Angiosperm

A flowering plant. Angiosperms are the most recently evolved of the plant groups (bryophytes, seedless vascular plants, gymnosperms and angiosperms), but they have adaptations that allowed them to conquer the world. They are now the dominant plant type. Napoleon could have learned a thing or two from angiosperms.

Apical

Refers to the tip of the plant. If you climb to the top of the mountain, you’re at the apex. Same idea with a plant, but apical can refer to both the tip of the shoots and the tip of the roots.

Apical Meristem

A zone at the tip of a shoot or root where lots of cell division occurs, adding to new growth. Consider it one of the main construction zones of the plant.

Bud Scale

Modified leaves that form a scale, covering a new bud. Bud scales protect buds before they open up and grow into shoots.

Cohesion-tension Theory

The explanation for water movement in the xylem. The water is under tension, because it is evaporating out of the leaves. Cohesion makes water molecules stick together, so a column of water moves as one entity instead of many molecules moving separately.

Collenchyma

A cell type that functions in supporting the plant. You can find an example of collenchyma cells in stalks of celery—those wispy strands running the length of the celery are collenchyma cells.

Cotyledon

a seed leaf. The cotyledon(s) nourishes a growing seedling, like a bottle nourishes a baby.

Epidermis

The outermost layer of cells. Humans have this layer too, but ours aren’t green.

Eudicot

One of two major groups of flowering plants. Formerly just called "dicot," eudicots have two cotyledons, have floral parts in multiples of four or five, and have networks veins on their leaves. Compare to monocot.

Fertilization

The fusion of two haploid gametes to make a diploid zygote.

Gamete

A reproductive cell. Male gametes are sperm; female gametes are eggs. Gametes are haploid (N), meaning they only have one set of chromosomes. When a sperm and egg meet, they form a diploid zygote.

Gametophyte

A gamete-producing plant. Gametophytes are haploid (N). In mosses and ferns, the gametophyte generation is independent. In gymnosperms and angiosperms, gametophytes are greatly reduced and dependent on the sporophyte.

Gymnosperm

A non-flowering seed plant, such as a pine tree, redwood or fir tree.

Heartwood

The innermost, hardest wood of a tree. Compare to sapwood.

Intercalary Meristem

A region of cell growth at the base of nodes and leaves. Only found in monocots.

Lateral

Refers to the side of the plant. See lateral meristem, below.

Lateral Meristem

A zone of high cell division activity that creates width, also known as secondary growth. Both the vascular cambium and the cork cambium are lateral meristems. Compare to apical meristem.

Macronutrient

One of the six nutrients that plants need in large quantities. Primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K). Secondary macronutrients, needed in less quantity, are calcium (Ca), sulfur (S) and magnesium (Mg).

Micronutrient

A nutrient that is essential to plant nutrition but only in small quantities.

Meristem

An area of the plant where lots of cell division occurs. There is a lot of hustle and bustle in the meristems, because new cells formed in a meristem are continuously adding to length or width of the plant.

Mesophyll

The middle layer of leaf tissue. If a leaf were a sandwich, the lower and upper epidermis would be the bread and the mesophyll would be meat or cheese.

Monocots

A group of plants that are all evolutionarily related, and are distinguished by the fact that they have one cotyledon (seed leaf). Just because they only have one seed leaf doesn’t make them inferior—some of the most important food plants are monocots, such as grasses. Other monocots, such as orchids and lilies, are prized for their beauty. Other traits monocots share are shallow, fibrous roots; floral parts in multiples of threes; and parallel veins.

Net Venation

The web-like pattern of veins in the leaves of eudicots.

Parallel Venation

The pattern that veins make in monocot leaves: all the veins are parallel to each other. Grasses, palm leaves and corn stalks all have parallel venation. Go ahead and take a look next time you see some grass.

Parenchyma

The most common plant cell type. Parenchyma cells are involved in storage, wound repair, and are the site of photosynthesis.

Phloem

The vascular tissue that carries sugars and other nutrients throughout the plant. Phloem cells are alive when functional, and form long tubes.

Phyllotaxy

The arrangement of leaves around the plant stem. A plant maximizes the solar energy it receives by using feng shui to arrange its leaves.

Pollen

The dispersal unit for plant sperm. Pollen houses the male gametophyte and carries it to new places. The amount of pollen plants make depends on how they are pollinated: wind-pollinated plants make much more pollen than animal-pollinated plants, because they will inevitably lose some. Animal-pollinated plants can afford to make less pollen since they have dedicated pollen transfer agents (pollinators) that they entice with sweet nectar rewards.

Pollinator

An animal that transfers pollen between plants of the same type, whether willingly or unwillingly. Flowering plants have devised lots of tricks to deceive pollinators. Orchids are notorious tricksters, as their flowers can look like female bees. When a male bee sees the flower, he tries to mate with it, transferring pollen in the process. The bee doesn’t even get nectar in return for its effort!

Pressure-flow Hypothesis

The explanation for phloem movement. Phloem flows from areas where sugar is made to areas low in sugar because of turgor pressure.

Primary Growth

Growth that elongates the plant, but doesn’t make it wider. Primary growth originates at one of the apical meristems (shoot or root).

Rhizome

A specialized stem that grows underground and functions as a storage organ. Rhizomes are often confused with roots by the naïve observer. However, you Shmoopers will be able to tell your friends that potatoes and ginger are rhizomes, but onions are not.

Roots

The organs responsible for getting nutrients from the soil, among other things. Dig in the ground a little bit, and you’ll probably come across one of these pretty soon. You may even see some aboveground, if there are large trees growing near any of your sidewalks. Did you know that tree roots are the main cause of water pipe damage? Roots are surprisingly strong, and they don’t always grow underground, either.

Root Cap

A protective cover for the tip of the root. No, this isn’t what plants wear to baseball games, even if they’re rooting for the home team. (It’s okay to groan here.) Root caps protect the root apical meristems and allow roots to burrow through rocky soil, water mains, and whatever else they can get their dirty little hands on.

Sapwood

The living, outermost wood in a tree. Sapwood is where the xylem carries water through the tree, and is also softer than the hard heartwood in the center of the tree.

Sclerenchyma

A rigid cell that functions in supporting of the plant.

Secondary Growth

Adds width to a plant. Secondary growth originates at a lateral meristem and helps the plant stem widen.

Seed

A little bundle of joy containing genetic material to make a new plant, and nourishment for the baby plant as it starts growing. Higher plants (gymnosperms and angiosperms) have seeds, but more primitive plants such as ferns and mosses do not.

Sieve Plate

The porous cell walls in between two sieve elements (phloem cells). Sieve plates have holes in them, allowing liquid to move from one sieve element to the next. You wouldn’t want to eat dinner on a sieve plate.

Spore

A haploid cell produced through meiosis in the sporophyte. Spores are the haploid asexual offspring of sporophytes, and arise through meiosis. Unlike gametes, spores don’t need another cell to grow into a new plant, even though they are haploid. Spores divide through mitosis and grow into gametophytes.

Sporophyte

A diploid plant that produces spores. All vascular plants (ferns, gymnosperms, angiosperms) have sporophytes as their dominant (and visible) generation.

Springwood

Wood that is made with big cells during times when water and nutrients are bountiful, such as in the spring.

Stoma

A pore in the epidermis of a leaf or stem that allows gas exchange. The plural of stoma is stomata, but one stoma can also be called a stomate. Stomata are controlled by guard cells.

Sugar Sink

An area of the plant that receives sugars from the phloem.

Sugar Source

An area of the plant that produces sugars, such as leaves, or releases sugars from storage, such as roots during certain parts of the year.

Summerwood

Wood made later in the year than springwood, when water and nutrients are not as plentiful. Cells in summerwood tend to be smaller than those in springwood.

Tissue

A group of cells that function together in some way.

Tracheophyte

A vascular plant. Or in other words, a plant with a plumbing system. These plants don’t exactly have running water or bathtubs, but they do have a system to move water around their bodies.

Trichome

A small hair that arises from an epidermal cell and functions in protection and prevention of water loss.

Vascular

Refers to the plant’s circulatory system. Plants vascular systems are made up of xylem and phloem.

Venation

The arrangement of veins in a leaf. This can help classify a plant in its taxonomic group.

Xylem

The vascular tissue that transports water and is dead when functional.

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