IB Biology -- Plants

Veins

Location: Distributed throughout the leaf to transport raw materials and products of photosynthesis. Veins occur roughly in the middle of the leaf so that they are near all the leaf cells.

Spongy Mesophyll

Location: just superior to the stomata, bottom portion of the leaf Loosely packed cells with few chloroplasts; air spaces Allows for continuous channels for gas exchange

Stomatal Pores

Location: Bottom surface of the leaf. The stomatal pore can either open (left) or close (right) depending on the environmental conditions and mainly helps to absorb water. This area receives less light so as a result the temperature here is lower than on the upper surface. The lower temperature minimizes water loss from the pores and the plant, so the lower epidermis usually has thinner cuticles than the upper epidermis. The positioning of the epidermis is such that the remaining structures of the leaf are protected and supported.

Sepals

Protect the developing flower while it is inside the bud

Water lost by transpiration is replaced by water from the vessels

Replacing water from the vessels maintains a high water vapor concentration in the air spaces of the leaf.

Style

Structure of the carpel that supports the stigma

Tropisms

growth or movement to directional external stimuli

C4 photosynthesis

have stomata that open during the day but take in CO2 more rapidly than non-specialized plants

Zone of elongation

is where cells are enlarging in size, corresponding with the G1 phase of the cell cycle

Zone of maturation

is where cells become a functional part of the plant

What light triggers activity from ATP-powered proton pumps in the plasma membrane of guard cells?

light from the blue part of the light spectrum triggers the active transport of potassium into the cell

Cotyledons

seed leaves that function as nutrient storage structures

Embryo root and embryo shoot

Become the new plant when germination occurs

IB 9.2.7 How do guard cells regulate transpiration?

By opening and closing the stomata.

Succulents

Cacti exist on water that the plant stores in fleshy, watery stems is a type of succulent. Succulents generally have fatter leaves to retain more water.

The vessel water column is maintained by cohesion and adhesion

Cohesion involves the hydrogen bonds that form between water molecules Adhesion involves the hydrogen bonds that form between water molecules and the sides of the vessels; adhesion counteracts gravity

Meristematic tissue

Composed of aggregates of small cells that have the same function as stem cells in animals

Ground tissue

Consists mostly of thin-walled cells that function in storage, photosynthesis, support, and secretion

How does humidity affect transpiration?

Decreasing humidity increases transpiration because of the greater difference in water concentration

IB 9.1.5 State that dicotyledonous plants have apical and lateral meristems.

Dicotyledonous plants have apical and lateral meristems.

What are the six things auxins are involved in?

1) stimulation of cell division in most meristematic tissue 2) differentiation of xylem and phloem 3) development of lateral roots in tissue cultures 4) suppression of lateral bud growth when present in the apical bud 5) stimulation of growth of flower parts 6) induction of fruit production without pollination

IB 9.2.4 How do terrestrial plants support themselves? (3)

1) thickened cellulose 2) cell turgor 3) lignified xylem.

Micropyle

A scar at the opening where the pollen tube entered the ovule

Vascular Bundles

A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues.

How does soil water affect transpiration?

If the intake of water at the roots does not keep up with transpiration, turgor loss will occur and the stomata will close. The transpiration rate will then decrease.

How does wind affect transpiration?

Increases the rate of transpiration because humid air near the stomata is carried away

How does temperature affect transpiration?

Increasing temperature causes greater transpiration because more water evaporates

Ovary

Base of the carpel, in which the female sex cells develop

What are the six steps of the stem causing it to bend towards a light source?

1) Auxin is produced by all cells in the stem on the side towards the light source 2) Auxin moves by efflux pump action into the nuclei of cells on the side to the stem opposite the light 3) The auxin and a receptor in the nuclei form a complex that activates a proton (hydrogen ion) pump 4) Proton pump moves hydrogen ions into the spaces of the cell wall 5) Hydrogen ions cause a drop in pH, resulting in the hydrogen bonds between cellulose fibres of the cell wall breaking 6) This results in the elongation of the cells on the side away from the light

What are the 4 steps of the pressure-flow hypothesis?

1) Loading of sugar into the sieve tube at the source. This reduces the relative water concentrations in the sieve tube members, which causes osmosis in the surrounding cells 2) Uptake of water at the source causes a positive pressure, referred to as hydrostatic pressure, in the sieve tube, which results in a flow (bulk flow) of the phloem sap 3) Hydrostatic pressure is diminished by the removal of sugar from the sieve tube at the sink. Sugars are changed at the sink to starch. Starch is insoluble and exerts no osmotic effect. 4) Xylem recycles the relatively pure water by carrying it from the sink back to the source.

What are the ways halophytes have adapted to their salty environment?

1) Many become succulent by storing water, thus diluting the salt concentrations 2) Several species, for example the mangrove, secrete salt through salt glands 3) Some species are able to compartmentalize Na and Cl in the vacuoles of their cells, thereby preventing NaCl toxicity 4) Sunken stomata on thickened leaves reduce water loss by creating a higher humidity near the stomata. The thickened leaves often include a more developed cuticle to minimize water loss 5) Surface area of the leaves is reduced

What are six traits about dicots?

1) Netlike venation pattern in the leaves 2) Four of five flower parts, or multiples of four or five 3) Seeds contain two cotyledons (seed leaves) 4) Vascular bundles arranged as a ring in the stem 5) Root system involves a taproot 6) Pollen grain with three openings

What are six traits about monocots?

1) Parallel venation (the system of veins) in leaves 2) Three flower parts, or multiples of three 3) Seeds contain only one cotyledon (seed leaf) 4) Vascular bundles arranged throughout the stem 5) Root system mainly fibrous 6) Pollen grain with one opening

What are some ways in which plants have adapted to reduce transpirational water loss?

1) Small, thick leaves reducing surface area 2) Reduced number of stomata 3) Stomata located in the crypts or pits on the leaf surface 4) A thickened, waxy cuticle reduces water loss by acting as an impenetrable barrier to water 5) Hair-like cells on the leaf surface causes higher humidity near the stomata

What is necessary for the germination of a seed?

1) Water to rehydrate dried seed tissues 2) Oxygen to allow aerobic respiration to produce ATP 3) An appropriate temperature for the seed is necessary for enzyme action

What are the three major processes that allow mineral ions to pass from the soil to the root?

1) diffusion of mineral ions and mass flow of water in the soil that carries these ions 2) the action of fungal hyphae 3) active transport

IB 9.2.2 List ways in which mineral ions in the soil move to the root.

1) fungal hyphae (mutualism) 2) mass flow of water in the soil carrying ions 3) the diffusion of mineral ions.

Lateral meristems

Allow growth in thickness of plants. This is referred to as secondary growth. Most trees and shrubs (woody plants) have active lateral meristems. 1) vascular cambium, which produces secondary vascular tissue and lies between the xylem and the phloem in the vascular bundles, on the inside it produces secondary xylem, which is a major component of wood, and on the outside it produces secondary phloem 2) cork cambium, which occurs within the bark of a plant and produces the cork cells of the outer bark

9.3.6 Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.

Flowering in long-day and short-day plants is controlled by a pigment called phytochrome. This pigment exists in two forms, Pr and Pfr, which can be converted into each other. The Prform is the inacctive form and absorbs red light with a wavelength of 660 nm. When Pr absorbs red light it is rapidly converted to the active Pfr form. The Pfr form absorbs far red light with a wavelength of 730 nm and then rapidly converts to the Pr form again in day light. Normal day light contains more light of wavelength of 660 nm rather than 730 nm. This means that in normal day light, there is more Pfr than there is Pr. The Pr form is the more stable of the two and therefore during the dark hours Pfr is slowly converted back into Pr. The amount of Pfr remaining after the dark nights is most likely the way plants can time the length of dark periods. If the dark period is short, this means there will be a lot of Pfr as not much of it will have converted back into Pr. If the dark period is long, less Pfr will be available as most of it will have been converted back into Pr. Furthermore, Pfr promotes flowering in long day plants and inhibits flowering in short-day plants. During long dark periods (autumn-winter) short day plants will flower as most of the Pfr has been converted back into Pr in the morning. Long-day plants flower in the shorter dark periods (spring-summer) as enough Pfr remains in the morning to promote flowering.

Apical meristems

Location: roots and stems Shoot apex produces new tissue and causes primary growth through the process of mitosis and cell division. Primary growth allows the root to extend throughout the soil. It also allows the stem to grow longer and so increases exposure to light and carbon dioxide. This type of growth results in herbaceous, non-woody stems and roots.

Palisade Mesophyll

Location: upper portion of the leaf, where light is most available The cells of this region are chloroplast rich to allow maximum photosynthesis.

Phloem

Made up of sieve tube members and their companion cells. Sieve tube members are connected by sieve plates, which have pores that allow the movement of water and dissolved organic molecules throughout the plant. Water and food transported in various.

Vascular tissue

Made up of xylem and phloem that carry out long-distance conduction of water, minerals, and nutrients within the plant, and provide support

Phloem sap

Organic molecules that are dissolved in water - sugars (sucrose is the most common, and sugars account for most of the phloem) - amino acids - plant hormones -small RNA molecules

Auxin efflux pumps

Move the auxin out of the cells closer to the light, using ATP as the energy source.

Translocation

Movement of organic molecules in plants

Alternation of generations

Occurs between the gametophyte generation, which is haploid, and the sporophyte generation, which is diploid.

Petals

Often colorful to attract pollinators

IB 9.2.6 Explain how water is carried by the transpiration stream, including the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation.

Once water has been taken up by the roots it is pulled upwards into the leaves where it evaporates, a process called the transpiration stream. This transpiration stream occurs in xylem vessels and the movement of water is passive. Mature xylem vessels are long dead structures made up of cells arranged from end to end. The cell walls between the adjacent xylem cells are broken down and the cytoplasmic content dies to form a continuous tube. The cells also lack a plasma membrane which allows water to enter the vessels freely. In addition, they also contain pores in the outer cell walls which allows the movement of water out of the vessels and into the surrounding cells of leaves. The outer cell walls contain thickenings which resemble spirals or rings impregnated with lignin which makes the vessels strong and able to withstand low pressures. Low pressure (suction) is created in the xylem vessels when water is pulled out of the transpiration stream via evaporation of water vapour from the spongy mesophyll cell walls in the leaves. Heat from the environment is necessary as it provides the energy required for the evaporation of water. The low pressure causes more water from the roots to be pulled upwards through the xylem tubes, this is called transpiration pull. Transpiration pull works due to the cohesion of water molecules. Hydrogen bonds form between the water molecules allowing the formation of columns of water which are not easily broken by the low pressure. In addition, adhesion also plays a role in maintaining transpiration pull. The water molecules adhere to the walls of the xylem vessels preventing the columns of water from breaking. So to conclude, the structure of xylem vessels, transpiration pull, cohesion, adhesion and evaporation are all important in the carrying of water by the transpiration stream.

Dermal tissue (epidermis)

Outer covering that protects against physical agents and pathogenic organisms, prevents water loss, and may have specialized structures for various purposes

Anther

Part of the stamen that produces the male sex cells (pollen)

9.2.11 Outline the role of phloem in active translocation of sugars (sucrose) and amino acids from source (photosynthetic tissue and storage organs) to sink (fruits, seeds, roots).

Phloem tissue transports sugars and amino acids from sources which include photosynthetic tissue (leaves and stems) and storage organs, to sinks which include the fruits, seeds and roots of the plant. This transport is known as active translocation and requires energy.

9.2.8 What causes the closing of the stomata?

Plant hormone abiscisic acid

Auxins

Plant hormones that cause the positive phototropism of plant shoots and seedlings. Auxins appear to increase the flexibility of plant cell walls in young developing shoots. This enables cell elongation on the side of the shoot necessary to cause growth towards the light.

Source

Plant organ that is a net producer of sugar, either by photosynthesis or by hydrolysis of starch (Leaves) tubers can be both sources and sinks

Sink

Plant organ that uses or stores sugars (Roots, buds, stems, seeds, and fruits)

IB 9.2.1 Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs.

Plant roots are very important for water and mineral ion absorption as well as the anchoring of the plant into the ground. Germination causes the embryonic root to break through the seed coat and start growing down into the soil. A whole root system then develops by the branching of this embryonic root into new roots, increasing the surface area for absorption. The surface area is further increased by the branching of root hairs from these roots.

Halophytes

Plants adapted to grow in water with high levels of salinity

CAM photosynthesis

Plants close stomata during the day and incorporate CO2 during the night

How does light affect transpiration?

Speeds up transpiration by warming the leaf and opening the stomata

Filament

Stalk of the stamen that holds up the anther

Stigma

Sticky top of the carpel on which pollen lands

9.3.5 Outline the metabolic processes during germination of a starchy seed.

The absorption of water is followed by the formation of gibberellin in the embryo's cotyledon. This stimulates the production of amylase which catalyses the breakdown of starch into maltose. This maltose then diffuses to the embryo for energy release and growth.

IB 9.2.3 Explain the process of mineral ion absorption from the soil into roots by active transport.

The concentration of mineral ions inside the plant's roots is a lot higher than that found in the soil. Therefore, mineral ions have to be transported into the roots via active transport. Protein pumps exist in the plasma membranes of root cells. There are many types of these protein pumps for the absorption of many different mineral ions. Active transport requires ATP production by mitochondria (aerobic cell respiration, oxygen is needed) and therefore the root cells also contain many mitochondria. The branching of roots and the formation of root hairs increases the surface area for the absorption of mineral ions by active transport.

IB 9.1.6 Compare growth due to apical and lateral meristems in dicotyledonous plants.

The plant meristem is a type of tissue composed of cells which are totipotent, cells that allows continuous growth and the formation of new organs. 1) Apical meristems are found at the tips of roots and shoots. 2) The apical meristem is responsible for the elongation of roots and stems. It allows the stem to grow taller and the roots to increase in length. Also, the shoot apical meristem allows the formation of new leaves and flowers. 3) The growth in height of the stem is important for photosynthesis while the lengthening of the roots is important for the plant to anchor deep into the soil and it is also vital for the uptake of water and nutrients found in deeper soil layers 4) The growth taking place at apical meristems is called primary growth. 1) Lateral meristems allow plants to also grow by increasing the diameter of their stems and roots. 2) Secondary growth 3) It allows extra xylem and phloem tissue production 4) It also provides stability for the plant to grow taller.

What are the four basic flower parts?

The sepals, petals, stamen, and carpel

Water moves down concentration gradients

The spaces within leaf have a high concentration of water vapor. Water moves from this location to the atmosphere, which has a lower water concentration.

Bulbs

These are modified leaf bases which serve as food storage and thereby enable the plant to survive adverse conditions.These leaf bases may look like scales or they may extend over and encircle the centre of the bulb (onion). At the base of the bulb, a modified stem can be seen. Roots grow from the underside of the base while the new stems and leaves arise from the upper side of the base. An example of a bulb is an onion bulb.

Tendrils

These are modified leaves. They are slim and provide attachment as well as support. In doing so they allow plants to climb upwards. They will rotate in the air until they reach a solid structure to which they can attach to. An example of plants with tendrils are grape vines.

Storage Roots

These are modified roots which serve as food storage. They also allow the plant to survive adverse conditions. An example of a storage root is a carrot.

Stem Tubers

These are modified stems which serve as food storage. The stem extends into the ground and forms enlarged, swollen structures which we call stem tubers. Stem tubers are used to store nutrients and therefore allow the plant to survive winter as well as other adverse conditions. They also serve as a mean of asexual reproduction as new plants develop from these stem tubers. An example of a stem tuber is a potato.

Guard Cells

Thickened area of the guard cell wall is oriented towards the stoma. Thus when the cells take in water and swell, they bulge more to the outside. This opens the stoma. When the guard cells lose water, they sag towards each other and close the stoma. Gain and loss of water in the guard cells is largely due to transport of potassium ions.

Water is pulled from the root cortex into xylem cells

This happens because of the tension created by transpiration and the maintenance of a continuous column of water

Tension occurs in the columns of water in the xylem

This is because of the loss of water in the leaves and the replacement o that lost water by xylem water. The water columns remain continuous because of cohesion and adhesion.

IB 9.1.7 Explain the role of auxin in phototropism as an example of the control of plant growth.

Tropisms are directional movement responses which occur due to external environmental stimuli. The direction of the stimulus affects the direction of movement. Tropisms can either be negative or positive. Positive tropisms are the directional movement towards the stimulus while negative tropisms are the directional movement away from the stimulus. Examples of stimuli causing tropisms in plants are gravity and light. Roots will grow towards gravity while the plant shoot will grow upwards in the opposite direction. The directional movement of plants in response to light is called phototropism. As seen with gravity, the plant's roots will grow away from the light, into the soil (negative phototropism) while the plant shoot will grow towards the light (positive phototropism). Positive phototropism seen at the tips of plant shoots is made possible due to plant hormones called auxins. Auxins are produced at the tips of plant shoots and then translocate to the darker side of the shoot tip and stem which is receiving less light. This translocation is made possible via auxin efflux carriers which are unevenly distributed in the plant tissue. Once auxins reach the shaded side of the plant, they cause the elongation of cells so that the shaded side grows faster than the brighter side, thereby promoting the bending of the plant shoot towards the light. Auxins do so by binding to auxin receptors on cells. The binding of auxin causes the transcription of certain genes within those cells and therefore the production of specific proteins which affect growth. Auxins allow the expelling of protons (hydrogen ions) into the cell walls of the cells on the shaded side, decreasing the pH inside the cells and in doing so activate specific enzymes which break down cellulose microfibrils within the cell wall. This loosens the cell wall and allows cell elongation. So to conclude, auxins are very important in the control of plant growth towards the light and thereby allow the plant to increase its rate of photosynthesis.

How does diffusion enable the movement of mineral ions into the plants?

When there is a higher concentration of a mineral dissolved in water outside the root than inside, the mineral ions may move passively, without cell ATP expenditure, into the root cells.

Xylem

Xylem transports water and minerals through vessel elements and tracheids, which are dead at maturity and have a primary and secondary cell wall. In pits, the secondary wall is thin or missing, allowing water to flow laterally.

Zone of cell division

new undifferentiated cells are forming, corresponding with the M phase of the cell cycle

Testa

tough, protective outer coat of seeds