IB 9: plant biology

What three processes does the success of plant reproduction depend on?

Pollination, fertilisation and seed dispersal

Define pollination

The transfer of pollen grains from an anther (male plant structure) to a stigma (female plant structure)

Define fertilisation

Fusion of a male gamete nuclei with a female gamete nuclei to form a zygote

Define seed dispersal

The process where the seed moves away from the parent plant, benefitting parent and offspring by reducing competition for resources

Where are the male and female nuclei in plant cells found?

Male- in the pollen grain

Female- in the ovule

Define germination

The emerging of an embryonic plant from a seed or spore after a period of dormancy

Which four main conditions does germination depend on?

Warmth, Oxygen and Moisture (and a suitable soil pH)

Which additional conditions for germination do some plants require?

• Fire

• Freezing

• Digestion

• Washing

• Scarification

What is mutualism (with an example)?

Mutualism is where both species benefit from an interaction, for example:

• The flowering plant gaining a means of sexual reproduction (via the transference of pollen between plants)

• The animal gaining source of nutrition (plants secrete a sugar-rich substance called nectar to attract pollinators)

What is the name of substance at the apex (growing tip) of the plant?

Meristem

What are the female parts of a plant and their functions?

• Stigma- the sticky, receptive tip of the pistil that is responsible for catching the pollen

• Style- elevates the stigma to help catch pollen

• Ovule- the structure that contains the female reproductive cells

• Ovary

What is the collective name given to the female reproductive organs of a flowering plant?

Carpel (or pistil)

What are the male parts of a plant and their functions?

• Anther: produces pollen

• Filament: supports the anther and makes it accessible to pollinators

What is the collective name given to the male reproductive organs of a flowering plant?

Stamens

What does the xylem transport?

Water and dissolved mineral ions

Features of the xylem

• Dead cells

• Lined with lignin

• Transport process (transpiration) is passive and requires no energy

• Transpiration only occurs in one direction

What does the phloem transport?

Photosynthetic sugars/organic solutes (specifically sucrose, which is made of glucose and fructose)

Features of the phloem

• Living cells

• Have sieve plates between cells

• Transport process (translocation) is two-directional

• Translocation requires energy

What type of cells does water evaporate from in the transpiration stream?

Spongy mesophyll cells

What is the testa of a seed?

An outer seed coat that protects the embryonic plant

What is the micropyle of a seed?

A small pore in the outer covering of the seed which allows for passage of water into the seed

What is the cotyledon of a seed?

Contains the food store of the seed and forms embryonic leaves

What is the epicotyl of a seed?

The embryonic shoot (also called the epicotyl)

What is the radical of a seed?

The embryonic root

What is the difference between a monocotyledonous plant and a dicotyledonous plant?

A monocotyledonous plant bears a single cotyledon (embryonic seed leaf) whereas a dicotyledonous plant has two

How can you identify whether a seed was monocotyledonous or dicotyledonous by looking at the adult plant?

• Monocots have narrow parallel veins and dicots have branching veins

• Monocots have petals in multiples of three and dicots have four or five petals

• Monocots have scattered vascular bundles and dicots have ringed vascular bundles

How is the structure of plant roots related to their function?

• Roots branch, giving increased surface area

• Root hairs further increase surface area

• Mineral ions are absorbed by active transport

How is the structure of a root hair cell related to its function?

• Large surface area (due to outgrowths/ extensions)

• Many mitochondria for aerobic respiration

• Protein pumps in the plasma membrane for active transport

• Association with fungal hyphae further increase surface area

Plasmodesmata

Junctions between plant cells with a continuous cytoplasm (gaps in the cell wall)

Symplast pathway

The pathway water takes from the root hair cell to the xylem through junctions called plasmodesmata between cells with continuous cytoplasm

Apoplast pathway

The pathway water takes from the root hair cell to the xylem through the cellulose fibres of touching cell walls

Why is the movement of water on the symplast and apoplast pathways considered diffusion and not osmosis?

Because the water particles do not pass through a membrane

What is the cortex in the context of plant roots?

The cells that water passes through on its journey between the root hair cell and the xylem

What is the Casparian strip?

A strip of wax that encircles the cell next to the xylem and prevents water from continuing on the apoplast pathway

What is the Casparian strip made of?

A type of wax called suberin

What happens to water when it reaches the Casparian strip?

Water on the apoplast pathway enters the cell and continues on the symplast pathway

Which layer of the roots do root hair cells belong to?

The epidermis (outermost layer)

What is the innermost layer of the roots called?

The endodermis

What are the three main types of lignin thickening?

Annular (rings), spiral (curly) or reticular (curly wurly)

What are the individual units of the phloem called?

Phloem sieve tube elements (nb. that they’re not called cells because the elements connected performing the same function)

What instrument is used to measure rate of uptake of water?

A potometer

Why is volume of water taken up by plant roots not always equal to volume of water that evaporates from leaves?

Some water can be used in the photosynthesis reactions inside the plant

Which four factors can change the rate of photosynthesis and how?

• Wind (more wind=more transpiration as water vapour is blown out of surroundings)

• Humidity (more humidity=less transpiration as the concentration gradient is shallower)

• Temperature (higher temperature=more transpiration as more evaporation)

• Light intensity (more light=more transpiration as stomata open for gas exchange for photosynthesis)

Xerophytes

Plants that are adapted for water conservation (ie. plants that show xeromorphic adaptations)

What are some examples of xeromorphic adaptations?

• Thick waxy cuticle to reduce transpiration

• Absence of stomata on upper epidermis

• Sunken stomata

• Leaf hairs limiting movement of air over leaf surface

• Modified leaves called spines

• Swollen stem for water storage

• Ridged structure (for self-shading)\

• Extensive root system with shallow roots and deep roots

What is meant by crassulacean acid metabolism (CAM)?

An alternative biochemical pathway to the Calvin cycle. In CAM, carbon dioxide can be absorbed at night, stored as an organic acid, and then released during the day. This conserves water as stomata only need to be open during the night.

Mesophytes

Terrestrial plants that are not adapted to either very dry or very wet conditions

Hydrophytes

Plants that are adapted to live in very wet conditions

What is phototropism?

The tendency for a plant to grow towards a light source

Which plant growth substance is associated with phototropism?

Auxin

How does auxin facilitate phototropism?

Auxin accumulates on the side of the plant furthest from the light and causes cells to lengthen.

Auxin causes the fibres of cellulose to become less rigid, meaning that the cell wall becomes more flexible.

This occurs because auxin causes Hydrogen ions to be pumped into the cell wall, lowering the pH and causing bonds between glucose molecules in cellulose to break.

Which two pumps are associated with phototropism?

H+ pumps and auxin pumps

What is the meristem?

Areas of undifferentiated tissue capable of indeterminate growth, found in plants (analogous to stem cells in humans)

What is the definition of a tropism?

The turning of an organism (usually a plant) in response to an external stimulus

What is meant by photoperiodism?

The developments of plants in response to changing relative lengths of days and nights (ie.seasonal flowering)

What are phytochromes?

Photoreceptor proteins found in plants which have a role in controlling flowering

In what two forms do phytochromes exist?

P_r (inactive)and P_fr (active)

P_fr is metabolically active while P_r is metabolically inactive. What does this mean?

Metabolically active substances promote or inhibit a process. Metabolically inactive substances do neither.

When does the conversion of P_fr into P_r occur, and is it fast or slow?

During the day, quickly

When does the conversion of P_r into P_fr occur, and is it fast or slow?

During the night (absence of light), slowly

What is the difference between apical and lateral meristems?

Apical meristems promote primary growth (lengthening) including production of leaves/flowers of the plant while lateral meristems promote secondary growth (widening) including the production of bark.