plants combination

Xylem

The tissue in plants responsible for transporting water and minerals from the roots to the rest of the plant.

Transpiration

The process by which water evaporates from the leaves of a plant, creating a pull that helps transport water and minerals through the xylem.

Vessel Elements/Members

Dead hollow cells in the xylem that transport water and solutes, with perforated end walls allowing for easy passage of water between cells.

Tracheids

Dead conducting cells in the xylem that are smaller in diameter than vessel elements, with tapered ends and pits for side-to-side conduction.

Fibers

Long, slender cells in the xylem that provide mechanical support and strength to the plant.

Parenchyma

Thin-walled living cells in the xylem that play a role in storage, metabolism, tissue repair, and regeneration.

Phloem

The tissue in plants responsible for transporting sugars and other organic compounds from the leaves to other parts of the plant.

Sieve Tube Elements/Members

Specialized parenchyma cells in the phloem that lack a nucleus and many other cellular components, connected by sieve plates and under positive pressure.

Companion Cells

Cells adjacent to sieve tube elements in the phloem that help coordinate their function and support their metabolic processes.

Seeds

Reproductive structures produced by plants, containing an embryo, seed coat, and endosperm, which can remain dormant until conditions are favorable for germination.

Dormancy

A period of growth inactivity in seeds, during which they remain viable but do not germinate. Different species have different requirements to break dormancy.

Germination

The process of initiating embryonic growth in a seed, resulting in the emergence of shoot and root structures.

Meristems

Regions of actively dividing cells in plants that contribute to primary growth and the initiation of new organs or branches.

Apical Meristem

Meristems located at the tips of roots and shoots, responsible for primary growth and the development of new tissues.

Intercalary Meristem

Meristems that occur between mature tissues, often at the bases of grass leaf blades, contributing to leaf elongation.

Lateral Meristem

Meristems responsible for secondary growth, increasing the width or girth of plant structures.

Reproduction

The process by which plants propagate and ensure the survival of their species. It includes both sexual and asexual mechanisms, such as vegetative reproduction.

Asexual Reproduction

The ability of plants to produce new individuals from vegetative parts such as stems, leaves, or roots without the involvement of gametes.

Succulent Plants

Plants, like cacti, that have the ability to reproduce asexually by growing a new plant from a detached segment of their stem.

Runners

Horizontal stems sent out by plants like strawberries that can develop into new plants by establishing roots and growing independently.

Rhizomes

Horizontal underground stems with short internodes that are thickened for storage.

Stolons

Horizontal stems, either aboveground or underground, with longer internodes and smaller diameter that can produce asexual plantlets.

Similar but different to runners

Tubers

Modified part of a stolon that is used for storage, such as potatoes.

Sexual Reproduction

The process of plant reproduction involving the fusion of male and female gametes.

Flower Anatomy

Complex structures in sexually reproducing plants that contain both male and female reproductive organs.

Pollination

The transfer of pollen from the anther to the stigma, which can occur through various mechanisms such as wind, insects, birds, or other animals.

Double Fertilization

A unique reproductive feature in flowering plants where one sperm cell fuses with an egg cell to form an embryo, while another sperm cell combines with polar nuclei to create endosperm.

Seed Formation

The development of a seed from the fertilized ovule, which contains the embryo, endosperm, and a protective seed coat.

Fruit Development

The maturation of the ovary into a fruit, which protects and aids in the dispersal of seeds.

Germination

The process by which a seed begins to grow and develop into a new plant.

Imbibition

The uptake of water through the seed coat, initiating metabolic processes within the seed.

Emergence of the Radicle

The first structure to emerge from the seed, the embryonic root, which anchors the plant and absorbs water and nutrients from the soil.

Shoot Growth

The emergence of the plumule, containing the embryonic shoot, which develops into the stem and leaves of the new plant.

Temperature and Light

Environmental factors that can influence germination, as some seeds require specific temperature or light conditions to trigger germination.

Seed Dormancy

A period of growth inactivity in certain seeds that allows them to survive adverse conditions, which can be broken by scarification, exposure to smoke compounds, or temperature fluctuations.

Hormones

Chemical messengers like gibberellins that regulate seed germination by stimulating embryo growth and mobilizing stored energy reserves in the endosperm.

What is an angiosperm and why is their reproduction considered sexual even in hermaphroditic species?

Angiosperms are flowering plants. Their reproduction is sexual because they can undergo meiosis to produce genetically unique gametes, even when one plant has both male and female organs.

How are male gametes produced in a flowering plant anther?

Microspore mother cells in the microsporangia divide by meiosis → 4 microspores → each becomes a pollen grain with a pollen tube cell and generative cell. The generative cell later divides into 2 sperm cells during pollen tube growth.

How is the female gamete (egg cell) produced inside an ovule?

A single diploid cell undergoes meiosis → 4 haploid cells, only 1 survives → that cell undergoes mitosis to form the 8-nucleate embryo sac → one cell becomes the egg; the rest assist fertilization then degenerate.

Name the 8 key flower structures and their functions (insect-pollinated flower).

Petals – attract pollinators;

Stigma – captures pollen;

Style – guides pollen tube;

Ovary – houses ovules → becomes fruit;

Ovules – house egg → become seeds;

Anther – produces pollen;

Filament – positions anther;

Sepal – protects flower during developmen

What three strategies do plants use to promote cross-pollination?

1) Wind, insect, or animal pollen transfer between plants;

2) Different maturation times for pollen and stigma (dichogamy);

3) Separate male and female flowers or separate male/female plants.

How do plants prevent self-fertilization via the S-locus?

The S (sterility) locus encodes enzymes that detect and degrade self-pollen, preventing it from fertilizing the egg. This enforces outcrossing and increases genetic diversity within the species.

Distinguish pollination from seed dispersal.

Pollination = transfer of pollen from anther to stigma (occurs before fertilization). Seed dispersal = scattering of mature seeds away from the parent plant after fertilization to reduce competition.

What happens to the embryo between seed formation and germination?

Embryonic growth is suspended (dormancy). Upon germination the seedling depends on food reserves in the cotyledons until leaves develop and photosynthesis begins.

What are phytohormones and name four examples?

Phytohormones are signalling chemicals that control growth, development, and stimulus response in plants. Examples: IAA (auxin), cytokinin, ethene (ethylene), abscisic acid.

Explain polar (directional) auxin transport via PIN proteins.

Cytoplasm is neutral (pH 7); apoplast is acidic (pH 5). In the cytoplasm IAA loses a proton → becomes IAA⁻ (trapped). PIN proteins export IAA⁻ into the apoplast where it is re-protonated → IAAH, which can diffuse into adjacent cells. PIN proteins on one cell side direct flow.

What is non-polar auxin transport?

Auxin can also travel through the phloem (sap) as nutrients are translocated — this is a non-directional route alongside polar transport.

Describe the full mechanism of positive phototropism step by step.

1) Phototropins detect more light on one side;

2) auxin moves from lighter to darker side;

3) high auxin causes H⁺ secretion into shaded cell walls;

4) lower pH loosens cellulose crosslinks;

5) expansins further disrupt cell wall;

6) shaded cells elongate faster;

7) stem bends toward light.

How exactly does auxin cause cell elongation (acid growth hypothesis)?

Auxin promotes H⁺ pump activity → H⁺ ions are actively transported (against concentration gradient, ATP required) from cytoplasm into the apoplast → cell wall acidifies → crosslinks between cellulose microfibrils weaken → microfibrils slide apart → cell elongates.

Where is auxin produced and what does it do?

Produced in shoot tips → transported to roots. Promotes meristematic differentiation, cell elongation, leaf development, apical dominance, and tropisms. Inhibits lateral (side) branch growth.

Where is cytokinin produced and what does it do?

Produced in root tips → transported to shoots. Promotes cell division (cytokinesis) and shoot growth. Inhibits leaf senescence and root development.

How do relative concentrations of auxin and cytokinin determine plant tissue type?

High auxin + low cytokinin → shoot formation. Low auxin + high cytokinin → root formation. Equal amounts → callus (undifferentiated filler tissue). They can act antagonistically or cooperatively.

What is apical dominance?

Auxin from the shoot apex is transported down the stem and suppresses growth of axillary buds into side branches. The further from the shoot tip, the lower the auxin concentration, so lower buds are more likely to sprout.

Explain the positive feedback loop between ethylene and fruit ripening.

Ethylene stimulates ripening changes (colour change, softening, sweetening, scent production). Ripening fruits produce more ethylene. This positive feedback synchronizes rapid ripening across all fruits on a plant — useful for attracting seed-dispersers all at once.

Why is synchronized fruit ripening advantageous?

It attracts seed-dispersing animals to the plant when all fruits are ripe simultaneously, maximizing seed dispersal. It is also useful for fruit farmers who can harvest entire crops at once.

Distinguish qualitative from quantitative observations in tropism experiments.

Qualitative = non-numerical, subjective (e.g. describing which way seedlings bend). Quantitative = numerical, objective (e.g. measuring angle of curvature with a protractor). Reliable data requires both accuracy (closeness to true value) and precision (repeatability)

What are the 6 features of an insect-pollinated flower?

1) Brightly coloured petals — attract & guide pollinators;

2) Scent — attracts pollinators;

3) Large spiky pollen — sticks to insects, protein-rich food;

4) Large sticky stigma — collects pollen;

5) Nectaries — secrete nectar as energy reward;

6) Nectaries positioned deep inside — insects must brush anthers/stigma to reach them.

What is a nectary and what role does it play in pollination?

A gland inside a flower that secretes nectar (sugar solution). Positioned deep in the flower so insects must brush past anthers and stigma to reach it, transferring pollen.

What are the four main strategies plants use to reduce self-pollination and promote cross-pollination? Give a named example for eac

1) Wind/animal pollen transfer between plants (e.g. Phyllostachys bambusoides — wind; vanilla orchid — Eulaema bees);

2) Monoecious — separate male and female flowers on the same plant (e.g. Zea mays/corn, Betula papyrifera/paper birch);

3) Dioecious — separate male and female plants entirely (e.g. Ginkgo biloba, Urtica dioica/stinging nettle);

4) Dichogamy — anthers and stigmas mature at different times (protandry = anthers first, e.g. foxglove; protogyny = stigma first, e.g. sacred lotus).

Distinguish monoecious from dioecious plants.

• Monoecious = separate male and female flowers on the same plant (e.g. corn).

• Dioecious = male and female flowers on entirely different plants (e.g. ginkgo) — self-pollination is impossible.

What is protandry vs protogyny and why do these promote cross-pollination?

• Protandry = anthers mature before stigma (e.g. foxglove).

• Protogyny = stigma receptive before anthers mature (e.g. sacred lotus).

• Both prevent self-fertilization by ensuring male and female structures aren't functional simultaneously.

What is hybrid vigour and why do plants benefit from cross-pollination?

Offspring of genetically unrelated plants tend to be healthier and grow more strongly than either parent, likely because heterozygosity reduces expression of harmful recessive alleles.

What is the genetic basis of self-incompatibility?

Controlled by the S-locus. A pollen grain cannot fertilize an ovule sharing the same S-allele — enzymes encoded by the S-locus recognize and degrade self-pollen. Practical example: single-variety apple orchards produce little fruit.

What are the 4 types of seed dispersal?

1) Explosive — mechanical force;

2) Fleshy/attractive — eaten by animals, seeds deposited in droppings;

3) Winged/leathery — carried by wind;

4) Hooks — attach to animal coats.

What are the 3 nuclei in a pollen grain and their roles?

2 are male gametes (sperm cells); 1 is the tube nucleus which controls pollen tube development.

: What is inbreeding depression?

Reduced fitness in offspring from related parents — causes premature death, failure to thrive, and infertility. Self-pollination increases the chance harmful recessive alleles become homozygous.

What happens to the 4 haploid cells produced during female gamete formation?

3 degenerate and are reabsorbed. The 1 survivor divides by mitosis 3 times → 8 haploid nuclei, one of which becomes the egg. The rest assist fertilization and embryo development.