SBI3U Final Exam Review : Unit 7 - Plants

Angiosperm

A vascular plant with seeds enclosed in protective tissue

Gymnosperm

A vascular plant with non-enclosed seeds

Photosynthesis Equation

6H₂O + 6CO₂ + sunlight → C₆H₁₂O₆ + 6O₂

Significance of photosynthesis

It turns energy from sunlight into chemical energy stored in molecules. It creates food for plants, making them important producers in the food chain. It allows plants to be a carbon sink and release oxygen so all cells can undergo cellular respiration.

Methods of seed dispersion

Animals

Wind

Water

Gravity

Explosion

Seed dispersion through animals

Seeds can be eaten or carried by animals, which are later dispersed through droppings, burying, or falling off

Seed dispersion through wind

Plants with lighter seeds can have their seeds blown off of the plant and away from the parent, such as dandelions

Seed dispersion through water

In plants that grow near water, their seeds can float or be swept away from the parent plant

Seed dispersion through gravity

Seeds can fall directly from a parent and roll away or be buried

Seed dispersion through explosion

When some fruits ripen, they shoot seeds outwards from the plant

Xylem

Vascular tissue that transports water and minerals from the roots to the leaves

Structure of xylem

It is made of tracheid cells, as well as vessel elements in angiosperms. When these cells mature, their living contents die, leaving the dead cell walls in place.

Factors influencing water movement in xylem

Diffusion according to concentration gradients

Root pressure

Transpiration pull due to cohesion and adhesion

Osmosis in plants

Water moves by diffusion according to concentration gradients in the plant. The roots have a greater solute concentration and a lower water potential than the soil, so water moves into the root xylem. This solute gradient is maintained through active transport. This creates a high pressure at the roots

Root Pressure

The mechanism by which positive pressure in the roots moves water upwards in a plant

Transpiration Pull

Transpiration happens at the leaves of a plant. This creates a negative pressure that pulls the water and creates tension. Because water sticks to itself and the xylem walls through cohesion and adhesion, the water column in the xylem is pulled upwards to replace the transpired water molecules.

Cohesion

The force of attraction between water molecules

Adhesion

The force of attraction between water and other surfaces

Phloem

Vascular tissue that transports organic nutrients, often from the leaves to the roots, but also from roots and mature leaves to new leaves

Structure of phloem

It is made of sieve tube elements, which have sieve plates with holes and no nuclei. Beside them are companion cells, which carry out life functions to maintain both cells

Translocation

The transport of sucrose and other organic molecules through the phloem of a plant

Pressure-Flow Model

A model that explains how organic molecules move from source to sink through phloem in a flowering plant

Source

Any place in a plant where the sugars enter into sieve tubes

Sink

Any region in a plant where sugars are used or stored, such as roots, fruits, or flowers.

Translocation of sugars in plants

Nutrients are pumped by active transport into the phloem at the source, so water moves in as well. This creates a high pressure near the source phloem, and it pushes the sucrose-rich solution towards the sinks, where there is lower pressure. The sucrose is removed from the sink phloem and moved to the sink with active transport.

Xylem and phloem in trees

The vascular bundles are around the edges of the stem, just under the bark. Every year, the vascular cambium produces new vascular tissue on the outside ring. The inside dies and becomes the heartwood in the centre. The xylem is closer to the centre as sapwood, and the phloem on the outside.

Monocot

A major cluster of flowering plants that have one cotyledon

Dicot

A major cluster of flowering plants that have two cotyledons

Cotyledon

A structure within a plant embryo that helps to nourish the plant as it first starts to grow; also known as a seed leaf

Seeds in monocots

Has one embryonic seed leaf/cotyledon

Seeds in dicots

Has two embryonic seed leaves/cotyledons

Structure of roots

Root hairs on the outside to increase the surface area for the absorption of important minerals, such as nitrates, phosphates, and potassium

Apical meristem on the root tips, underneath the root cap, to allow the roots to grow

The cortex is under the epidermis, and all materials entering the root must pass through it

Vascular bundles inside

Roots in monocots

Typically fibrous root systems

Fibrous Root

A root system made up of many small branching roots

Roots in dicots

Typically taproot systems

Taproot

A root system made up of a thick root with a few smaller lateral branching roots

Leaves in monocots

Veins are usually parallel to each other along the length of the leaf

Leaves in dicots

Veins are palmate of pinnate

Vascular bundles in stems of monocots

Scattered throughout ground tissue

Vascular bundles in stems of dicots

Arranged in a ring

Vascular bundles in roots of monocots

Arranged in a ring

Vascular bundles in roots of dicots

Xylem is arranged in a star shape with phloem surrounding it

Germination in monocots

The seed begins with a radicle and a coleoptile. A first leaf and a primary root grow out of the radicle. The first leaf remains at the bottom of all of the leaves that grow after. Adventitious roots begin to grow.

Germination in dicots

A hypocotyl emerges from the seed coat. Primary roots grow underground as the cotyledon begins to grow and form leaves. Secondary roots grow, and the cotyledons wither as two leaves grow out of the epicotyl.

Stomata

Small openings, usually in the leaf, that allows gas exchange to occur

Guard Cell

A specialized epidermal cell; functioning in pairs, they regulate the opening of the stomata.

Function of stomata

They permit gas exchange and transpiration to occur. They open and close in response to external factors, such as light and CO₂ levels, to maintain homeostasis in the plant.

Flaccid

Drooping or inelastic through lack of water.

Turgid

Swollen due to being filled with water

Times when stomata is open

It starts opening in the morning and opens again in the afternoon/evening. They open when:

It is light because photosynthesis requires gas exchange to occur

CO₂ levels are low because it means that photosynthesis is happening, and it needs more CO₂ through gas exchange

Soil water is high because the plant can take in more water to make up for the water lost during transpiration

How stomata open

K+ ions are pumped into the guard cells by active transport. Water follows due to osmosis, creating turgid cells that open the stomata

Times when stomata is closed

It closes in the night and at noon. They close when:

It is dark because photosynthesis isn’t happening, so it is not worth risking water loss and dehydration

CO₂ levels are high because it signals that photosynthesis is not occurring, so no gas exchange is happening

Soil water is low because the plants are not taking in water, so it minimizes water loss

How stomata close

K+ ions are moved out of the guard cells by active transport. Water moves out due to osmosis, creating flaccid cells that close the stomata.

Transpiration

The process in which water evaporates from the inside of a leaf to the outside through stomata

How transpiration controls homeostasis in plants

It helps move water through the plant by transpiration pull. As well, it helps maintain a low water potential at the leaves of the plant, so water will continue to move to the leaves. It also helps to move dissolved minerals through the plant. It helps with temperature regulation. It moves water to the leaves, which is necessary for photosynthesis.

Structure of a leaf

The topmost layer has a waxy cuticle. Underneath is the upper epidermis, palisade mesophyll, and an air space. The air space contains spongy mesophyll and vascular bundles. Underneath the air space is the lower epidermis which forms the bottom of the leaf. This contains the guard cells and stomata.

Waxy Cuticle

A layer on the epidermis of a leaf that is secreted by epidermal cells

Palisade Mesophyll

The layer of cells where the most photosynthesis takes place, immediately below the epidermis

Spongey Mesophyll

The layer of irregularly shaped, loosely packed cells below the palisade mesophyll layer

Adaptations of leaves in different habitats

Plants in cold environments have small, needle-like leaves to withstand harsh weather and retain water.

Plants in hot environments have succulent leaves to conserve water.

Aquatic plants have stomata on the upper side of the leaf to facilitate gas exchange with the air.

Plant adaptations to extreme climates

Plants in extreme heat, such as cacti, have small or nonexistent leaves to reduce the amount of surface area where transpiration may occur.

Potometer

A device used for measuring the rate of water uptake of a leafy shoot which is almost equal to the water lost through transpiration

Potometer Lab Set-Up

While submerged in water, attach a piece of plastic tubing to a pipette, and use a syringe to eliminate all bubbles

Cut a plant stem attached to leaves under water, and insert the end of the stem into the plastic tubing

Use the clamp on a ring stand to hold the pipette and the tubing with the leaves upright

Expose the potometer to either the ambient room temperature, wind, light, or a humid bag

Over 20 minutes, record how much water has transpired, in hundredths of a millilitre, every 2 minutes

Why is the potometer lab set up while submerged in water?

To avoid breaking the water column in the xylem that allows transpiration pull to occur

Different treatments of the potometer lab

Wind (fan), Sun (light), Ambient Room (control), and Humidity (damp plastic bag)

Expected results of the potometer lab

The wind would have the greatest transpiration rate because it constantly moved the air, which has a lower water concentration, away from the surface of the leaves, meaning that water would continuously move out of the leaves due to osmosis

The second greatest rate would be light because it aids in evaporation and the opening of the stomata

Ambient room temperature would be third

Humidity would have the lowest rate because the increased concentration of water outside of the leaves means less water would transpire due to osmosis

How to solve for the total surface area of the leaves in the potometer lab

Find the weight of a known area in cm² of leaves to find the density

Convert the area of the density to m² by dividing cm² by 10,000

Weigh all of the leaves used in the experiment

Divide the weight by the density to find the area of leaves used in the experiment in m²

Transpiration Rate

(mL transpired)/(m² of leaves)/(minutes passed)

Why couldn’t the bark of the branch be damaged in the potometer lab?

It would damage the sapwood/xylem tissue, which would prevent water from being able to move through