SBI3U Plants

Succession

Gradual change in species composition within an ecosystem

Primary Succession

Succession from an area that had no soil, no plants, and no other life. This can include a lava flow.

Secondary Succession

Succession that happens after a disturbance in an ecosystem. This succession is usually much faster than primary succession since there is already organic matter to work with.

Positive effects of human activity on succession

1. Traditional and prescribed burns can bring back native vegetation into an ecosystem
2. Selective cutting is better than clear cutting as it still allows the ecosystem to remain at a later stage in succession
3. Naturalization: planting of native plants and removal of non-native plants

Negative effects of human activity on succession

1. They can cause disturbances leading to secondary succession (forest fires, deforestation, mining)
2. Some long-term actions can cause primary succession. (melting of glaciers which uncovers uninhabited land)

Leaves Function

Primary site of photosynthesis, site of gas exchange between interior of plant and the exterior environment.

Monocot vs. Eudicot Leaves

Monocot: venation is parallel, the vascular tissue lies parallel with the others

Eudicot: venation is branched, the vascular tissue branches

Leaf specializations

• Some protect the leaves through physical (spikes) and chemical (poison) means
• Gymnosperms have specialized to prevent freezing during the colder months.

Stem Function

connect vascular tissue between the leaves and the roots
They also support other structures on the plant.

Monocot vs Eudicot Stem

Monocot: vascular bundles are found scattered in the stem
Eudicot: vascular bundles form a ring

Herbaceous stem

Softer, more flexible, and often green plant stems (not wood)
Mostly the monocots

Woody stem

Stem that contains wood and is thick and hard
Mostly the eudicots

Woody stem structure

• Inside (wood) made from old xylem.
• Between xylem and phloem is the vascular cambium (forms xylem on the inside and phloem on the outside)
• Outside of the phloem is the cork cambium and cork which make up the bark

What is wrong with removing a strip of bark?

It breaks the phloem at a certain section in the stem and sugar would not be able to travel throughout the plant.

Cambium and the two types

Cambium is a type of meristematic tissue in plants

1. Vascular cambium is found between xylem and phloem in roots and stems. It forms the xylem and phloem.
2. Cork cambium is found outside of the phloem in a woody stem and it forms the tough outer layer (cork)

What are potatoes

They are a form of stem specialization (underground stems) which help store water and starch and also help with reproduction

Function of Roots

anchors the plant and keeps it upright
collects nutrients and water from the soil or substrate

Root tip structure

There is the apical meristem that helps the root grow in length but there's also a root cap that protects the meristem.

Monocot vs Eudicot root

Monocot: the vascular bundles form a ring
Eudicot: the xylem forms an x in the centre and the phloem surrounds it.

Is the xylem larger than the phloem?

Yes, the xylem is usually in most cases larger than the phloem and is more visible on cross sections.

Root specializations (symbiotic relationships)

1. 80% of plants have mycorrhizae, which is a symbiotic relationship between plants and fungi. Fungi receive sugars and plants receive nutrients
2. Nitrogen fixing bacteria have a mutualistic relationship with plants. The plants get the nitrogen they need from the nitrogen fixing bacteria which adapt the nitrogen gas to the plants.

Two Types of Vascular Tissue

Xylem: transports water and soil nutrients
Phloem: transports sugars

Active and Passive Transport

Active: Requires ATP, goes against the concentration gradient
Passive: Does not require ATP, goes with the concentration gradient
(how substances move across cell membranes)

Xylem transport from ground to roots

• Water moves through osmosis (passive)
• Nutrients move through active transport

Water diffuses into the epidermis (outer layer), goes through the cortex (middle part) and into the endodermis (cover of the vascular cylinder)

Casparian strip

a strip surrounding the endodermis (covering of the vascular cylinder)
prevents water from diffusing back into the cortex

Transport in the stem (Xylem)

1. Capillary action: through cohesion and adhesion, water molecules stick together and move up together
2. Root pressure: water in the vascular cylinder pushes the rest of the water up.

Transport to the leaves (water)

Transpiration: the evaporation of water through the stomata
This pulls up the xylem sap and is the main driving force of transport in the xylem

Transport of sugars (sinks and sources)

Sugars move from sources (areas with high concentration of sugar) to sinks (areas with low concentration of sugar).
In most cases, the roots are the sink and the leaves are the source but it can switch depending on age or season

Source to Phloem

Sugars are actively transported due to a higher concentration in the phloem.
Water moves into the phloem through osmosis

Transport in the Phloem (Translocation)

Translocation: long distance transport of substances through the phloem
Appears to be caused by the difference in pressure in phloem cells and sink cells

Phloem to Sink

Sugars move passively (osmosis)
Water goes back to the xylem by osmosis

Asexual Reproduction in Plants

• Mitosis and cell division of the original plant in order to produce another plant.
• Structures on the leaves, stem ,or roots of a plant can help with reproduction
• The offspring are all clones of the parent plant

Examples of asexual reproduction in plants

1. Eyes on potato tubers are capable of growing into a new potato plant (stem)
2. Runners: strawberry plants have runners that grow another plant while still being attached to the original one (stem)
3. Bryophyllum plants can grow new plants (plantlets) on their leaves
4. Any part of the roots of dandelions can grow into a new species

Benefits of asexual reproduction in plants

1. Faster and takes less energy
2. If the parent is already very suited to the environment, then the offspring will also be successful
3. Requires only one parent, which is beneficial in the case of pioneer species
4. Plantlets have higher survival rate than seeds due to still being attached to the original plant.

Artificial (human) asexual reproduction in plants

1. Stem cutting in order to grow another plant
2. Tissue culture, for plants that do not reproduce asexually. A piece of the plant is placed in a tube with nutrients and/or growth regulators
3. Grafting (using scions and stocks)

Grafting

A form of artificial asexual reproduction where a scion of a desirable plant is attached to a stock of a plant that has a more resilient root system.

Flower parts

Carpel: female part ->

• Stigma: the top part where pollination happens
• Style: the pollen goes through this tube to make it to the ovary
• Ovary: where fertilization happens with the pollen and the ovules/eggs

Stamen: male part ->

• Anther: the top part where meiosis happens and pollen is located
• Filament: the tube to the anther

How is self-pollination sexual?

The male and female gametes still go through meiosis, where independent assortment and crossing over produce genetic diversity.

The offspring would not have the exact copy of the DNA of the parent.

Disadvantages of asexual reproduction

1. no genetic variation, all the offspring are the same so the population is very susceptible to any disease.

Apical meristem

Meristem that helps the plant grow in length (height and roots)
This is primary growth

Lateral meristem

Meristem that thickens the roots and stems (increase in diameter)

Primary growth

Growth produced by apical meristems, which lengthen stems and roots.

Secondary growth

Growth produced by lateral meristems, which thickens the roots and stem. (mostly only the woody stems, herbaceous have vascular cambium not cork cambium)

Produced by vascular and cork cambium is woody stems.

Macro and micronutrients

Nutrients. Macro ones are required in large quantities. The micro ones are required in smaller quantities.

Tropisms

Changes in the growth of a plant in response to a stimulus
Examples:

1. phototropism: in response to light
2. gravitropism: in response to gravity
3. thigmotropism: in response to touch stimulus

Phototropism

a growth response in plants to light. Usually a positive one where the plant grows in the direction of light.

Gravitropism

A growth response to gravity. This is negative for the shoot where the plant tries to grow in the opposite direction of gravity. It is a positive tropism for the roots which grow in the direction of gravity.

Thigmotropism

A growth response to touch

Plant Growth Regulators

Chemicals produced by plants that regulate growth and differentiation/specialization of cells

Various effects on plant growth and differentiation

Auxin

promote cell elongation
Mostly found in the shoot apical meristem

Ex. (phototropism) They move to the side away from the sun and elongate the cells there. The shoot would bend towards the sun.

Gibberellins

Induce flowering and fruit production

Spray induces flowering and fruit production in grapes but also elongates the fruit stems in grapes (grapes grow larger)

Cytokinins

Stimulate cell division

Ethylene

Gas that stimulates many plant stages, including fruit ripening

• Controlled when transporting fruit and can be used to ripen fruit

Abscisic Acid

Inhibits cell growth

• Increase in response to changes in photoperiod and temperature to maintain dormancy (leaves on trees)
• Sometimes used when shipping plants to minimize damage

Tissue Culture

Plant segments are moved between cultures with different growth regulators to first stimulate cell division then shoot differentiation etc.
Usually used with orchids

Seed function

Nourish and protect plant embryos

Parts of a seed

Seed coat on the outside separates and breaks when the seed germinates
Endosperm contains nutrients for the embryo and the plant to begin growing
Cotyledon is a seed leaf (monocots have one, eudicots have two)
Embryo is a tiny underdeveloped plant that begins to grow when conditions are right