Biology: Plant

Describe the process of Germination

the sprouting of a seedling from a previously dormant seed. · The seed is in a state of dormancy until environmental conditions (such as water, temperature, and light) are suitable for growth, then the seed breaks dormancy. · Water is the most important environmental "cue" that kick starts germination. · Imbibition - absorption of water by seed - causes it to swell up and break the seed coat. The water activates enzymes that catalyze metabolic processes to produce energy for growth process. · The radicle grows into roots that anchor the seedling in place · hypocotyl grows into the young shoot.

Plant Tissues → Ground Tissue

Provides structural support to the plant so it makes up most of a plant's mass. There are three types of ground tissue: 1. Parenchyma tissue cells act as filler tissue and make up the bulk of the entire plant. They have the thinnest cell walls of the three. → Pith is actually made of parenchyma tissue. It is the tissue found at the center of the root or stem. 2. Collenchyma tissue cells provide extra support to the plant, especially in areas where the plant is actively growing. They have irregular cell walls. 3. Sclerenchyma tissue cells provide the main structural support of the plant. They have the thickest cell walls of the three.

Every biogeochemical cycle has three main components:

Reservoirs Serve as major storage location for the element Assimilation Responsible for the element being taken up by plants and animals Release Process Returns the element back to its environment

Apical meristems → More specifically on growth at the root tips:

Root Cap - Covers and protects the apical meristem, allowing it to continue to grow and deeper penetrate the soil. Zone of Division - The continual division of the apical meristem cells forms a zone of division that's right above the apical meristem. Zone of Elongation - These cells then absorb water and elongate, forming a zone of elongation Zone of Maturation - These cells eventually differentiate into specific plant tissues, becoming part of the zone of maturation. *the apical meristem is constantly dividing and producing more cells that join the zone of division. Therefore cells that were once in the zone of division will become part of the zone of elongation, and cells that were once in the zone of elongation will become part of the zone of maturation.

What are root hairs?

Root hairs are little structures that project out of the epidermis of root cells. They increase the surface area of the epidermis cells which allow for greater water and nutrient uptake. Larger surface area means larger amount of space where the plant is in contact with and can draw substances from the soil.

Movement of Water: How does water get into the root in the first place?

Root pressure - pressure that builds up in the roots of plants. Particularly in moist soils, there exists an osmotic gradient which drives water into the root. The osmotic pressure pushes the column of water in the xylem upwards.

Seedless tracheophytes

Seedless tracheophytes include the phylums, lycophytes and pterophytes. Common examples include club moss, quillworts, fern, and horsetail. Ferns formed the first forests during the Carboniferous period. Although most are found in moist habitats, their vascular system allows them to successfully grow in more dry climates as well. · Most seedless tracheophytes are heterosporous (can produce both male and female spores). Seedless tracheophytes have flagellated sperm, meaning they can move on their own (they do not travel via wind or animal transport).

What connects Sieve cells and Companion cells?

Sieve cells and companion cells are connected via plasmodesmata (small channels that connect adjacent cells' cytoplasm), which allows for quick communication between the two.

What is the bark composed of?

The bark is the collective term for the outermost layer of the plant that includes the phloem, cork cambium, and cork The cork is the outermost layer of the bark and serves as a protective layer for the plant.

Flower Structures: Pistil

The female plant sex organ. It is composed of: stigma (top) style (tube down to the ovary) ovary which contains the ovule. Ovules contain the plant's female gamete (egg). When they are fertilized by pollen, they develop into the seeds.

Flower Structures: Petals

The petals on a flower are usually the most noticeable and distinguishable part of the plant. They function to attract animals to achieve pollination.

The presence of seeds in a plant shows great...

The presence of seeds in a plant shows great evolutionary advancement. Seeds are more resilient and durable (remember the nutritious endosperm and the protective seed coat!), allowing them to disperse more effectively and get planted and grow into a mature plant more successfully.

What forms the wood?

The secondary xylem and the pith form the wood

What forms the growth rings?

The vascular cambium continuously divides to produce new, additional secondary xylem year after year. This constant production of secondary xylem is what forms the growth rings that you see in the cross section of a tree. Older rings are closer to the center and newer rings are closer to the outside.

Secondary growth → vascular cambium

The vascular cambium is a ring of meristematic tissue located between the primary xylem (closer to center) and primary phloem (closer to edge). · Cells of the vascular cambium divide to produce new cells. · Cells produced on the inside of the vascular cambium ring become the secondary xylem → The secondary xylem and the pith form the wood. The vascular cambium continuously divides to produce new, additional secondary xylem year after year. This constant production of secondary xylem is what forms the growth rings that you see in the cross section of a tree. Older rings are closer to the center and newer rings are closer to the outside. · Cells produced on the outside of the ring become the secondary phloem → The secondary phloem contributes to the bark. The bark is the collective term for the outermost layer of the plant that includes the phloem, cork cambium, and cork. Unlike secondary xylem which grows and adds onto older xylem, secondary phloem replaces older phloem. Old bark is constantly shed and replaced by newly formed bark.

What are the three categories of plant tissues?

Tissue found in the root and stem of a plant can be broken up into three main categories: 1. Ground Tissue 2. Vascular Tissue 3. Dermal Tissue

What causes desiccation?

Transpiration poses the threat of drying out the plant via evaporation, called desiccation.

MOVEMENT OF FOOD: Source to Sink Theory

Vascular tissues transport material (such as water and sugars) throughout the plant. Materials are transported from the source (where the material is generated) to the sink (where the material is used). We will call this the source to sink theory. For example, phloem transports sugars from the leaves (source) to the roots (sink).

What type of plants undergo secondary growth?

Woody plants Herbaceous (non-woody) plants only undergo primary growth

What is Imbibition?

absorption of water by seed - causes it to swell up and break the seed coat. The water activates enzymes that catalyze metabolic processes to produce energy for growth process.

Meristems are...

areas of a plant where growth takes place via repeated cell division/mitosis. There are two types of meristem: apical and lateral.

All seed-bearing tracheophytes are

heterosporous

Secondary growth

horizontal growth of plant @ lateral meristems, which include the vascular cambium and the cork cambium. Cambium is another word for lateral meristematic tissue.

What are the three plant tropisms?

plant tropisms - growth in a certain direction Phototropism - the curving of a plant stem towards light. Gravitropism - the curving of a plant stem to oppose gravity. Thigmotropism - growth in response to contact (for example a vine growing up a wall).

Development is..

the growth of a seedling into a more mature plant.

The Casparian strip helps regulate

the type and amount of substances that can enter through the roots and travel to the rest of the plant (via the vascular tissues). It is made of a fatty, waxy substance that makes it impenetrable and is found inside the cell walls of plant roots. Therefore, all incoming substances that were travelling through the cell walls (which do not have a way of filtering substances) run into the impenetrable Casparian strip and are forced into the cytoplasm of the root cells. This way, the substances are forced to flow through the plasma membrane, which we know are semi-permeable and therefore do have a way of filtering substances.

Plant Hormone: Gibberellins

Affect stem and shoot elongation, elimination of dormancy of a seed, flowering, production of fruits, as well as leaf and fruit death.

Alternation of Generations

Alternation of generations is the ability for an organism to regularly exist in and alternate between both haploid and diploid forms. Fungi exhibit this property. Fungi can spend part of their life as a multicellular haploid organism and part of their life as a multicellular diploid organism. The top half of the diagram indicates which stages are haploid (n), meaning they have a single set of unpaired chromosomes. The bottom half of the diagram indicates which stages are diploid (2n), meaning they have two complete sets of chromosomes.

Alternation of Generations steps

1. Fusion of two gametes Start with the fusion of two gametes (at the very right of the diagram). From mammalian reproduction, you might know that the fusion of two gametes (specifically a sperm and an egg, both of which are haploid) produces a zygote(which is diploid). It makes sense that the fusion of two gametes (one from each parent) results in the generation entering the diploid state. 2. Zygote becomes a sporophyte via mitosis Memorize: A zygote becomes a sporophyte via mitosis. In this case, the zygote (parent cell) is 2n and the sporophyte (collective daughter cells) is also 2n. It makes sense that this happens through mitosis (and not meiosis) because we know in mitosis, thedaughter cells retain the same number of chromosomes as the parent cells. 3. Sporophyte produces spores via meiosis A sporophyte produces spores via meiosis. It makes sense that meiosis (the process that halves the number of chromosomes) of a sporophyte results in the generation entering the haploid state. → Note: sporangia are the structures in which spores are formed - located on the ends of sporophytes. Think of sporangia as the specific structures that are part of the bigger sporophyte. 4. Spore becomes a gametophyte via mitosis Memorize: a spore becomes a gametophyte via mitosis. In this case, the spore (parent cell) is n and the gametophyte (collective daughter cells) is also n. Again it makes sense that this happens through mitosis (and not meiosis) because we know in mitosis, the daughter cells retain the same number of chromosomes as the parent cells. In this case, the spore (parent cell) is n and the gametophyte (collective daughter cells) is also n. 5. Gametophyte produces gametes A gametophyte produces gametes. And we're back to the beginning. We're alternating states as we go from one generation to the next.

Angiosperm: Process of Fertilization

1. Pollen lands on stigma of another plant (or rarely, on its own plant) → tube cell elongates down the style towards the ovary, forming a pollen tube. 2. When the generative cell (male gamete or sperm) in the pollen travels down the pollen tube to the ovule (female gamete or egg), it divides to form two sperm cells (double fertilization) → One sperm cell fertilizes the ovule to form the seed (embryo). → The other combines with the polar nuclei of the ovule to form the endosperm (which acts as the food/nutrient store for the embryo) 3. In angiosperms, the ovary will turn into a fruit to help them reproduce (not provide them w/ food). →The fruit attracts and is eaten by an animal, then the seeds in the fruit pass through the animal's digestive system, and are 'deposited' in a new location. This spreads the genes of the angiosperm to new locations (called gene migration).

Two ways water can move between cells:

1. The apoplastic pathway is water movement outside the cell, with the cell wall. 2. The symplastic pathway is water movement through the cell's cytoplasm.

Plant Hormone: Ethylene

A gaseous hormone that increases the ripening of fruit. You may have heard the phrase that 'one rotten apple spoils the bunch' - it's because one rotten (overly-ripe) apple will release lots of ethylene. Because ethylene is a gas, it diffuses throughout the apple barrel and causes excess ripening of all the other apples.

Seed: Structure

A seed consists of: Seed coat: Hard outer layer that covers and protects the seed from various external forces (such as mechanical stress, too much water, fluctuations in temperature) Storage Material (usually food): In a seed provides nutrients to the embryo. Nutrients are stored in the form of endosperm Embryo: 1. Radicle - is the part of the embryo that develops into young root. It is the first to emerge from the seed coat and anchors the plant into the soil → Easy way to remember: both radicle and root start with the letter R The rest of the parts of the embryo (hypocotyl, plumule, and epicotyl) make up the young shoot (anything above the soil) 2. Hypocotyl - is the bottom region of the young shoot (above the roots but below the cotyledons) 3. Plumule - develops into the young leaves - In between the hypocotyl and the epicotyl 4. Epicotyl - develops into the very top region of the young shoot, or the shoot tip

Seed-bearing tracheophytes: Angiosperms

Angiosperms are seed-bearing tracheophytes that are also flower-bearing, and can produce fruit. Their seeds are protected, located in the fruit (considered the ovary of the plant). These are the most abundant type of plant living today. → Do not have flagellated sperm - all their sperm is wind or animal dispersed (often as pollen). Pollen is another example of evolutionary advancement - it is a highly efficient way of achieving fertilization. → Many angiosperms package their sperm in these small, easily-movable pollen grains, which can easily be picked off one flower and deposited on another flower (fertilization) by the wind or by an animal (like a bee). They have more opportunities and ways to fertilize and get fertilized. → Most angiosperms (and some gymnosperms) can exhibit double fertilization - when a female gamete is fertilized by two male gametes or sperm.

Apical meristems vs. Lateral meristems

Apical meristems Are at the very tips of roots and shoots → vertical growth → increase height In young/newly hatched seedling, vertical growth at apical meristems happen first before horizontal growth at lateral meristems of plant → primary growth Lateral meristems Growth in these areas → lateral or horizontal growth → increase width/thickness

Movement of Water: Water's upward movement can also be attributed to

Capillary action - an adhesive force between water molecules and the xylem vessels (two dissimilar surfaces). Adhesion is when dissimilar particles of surfaces are attracted to each other. Water is attracted to the xylem, and this causes the water to climb upwards within the vessel.

What are cotyledons and their function?

Cotyledons are the first leaves to appear on a seedling. They contain nutrients from the seed to feed to the growing seedling.

What are the five plant hormones?

Ethylene Auxins Cytokinins Gibberellins Abscisic acid

Plant Hormone: Abscisic acid

Functions in times of plant stress. It promotes dormant seeds (prevents premature opening), closes stomata (during drought), and inhibits growth. The dormancy caused by abscisic acid can be broken by gibberellin increase or environmental stimuli such as temperature or light.

Plant Tissues → Vascular Tissue

Functions to transport material to different parts of the plant. Vascular tissue transports material from the source (where the material is generated) to the sink (where the material is used). There are two different types of vascular tissue: 1. Phloem 2. Xylem

Seed-bearing tracheophytes: Gymnosperms

Gymnosperms are seed-bearing tracheophytes whose seeds are not protected (sometimes called a naked-seed). The most common example are conifers (cone-bearing plants). Examples of conifers include fir, spruce, aspen, redwood, and pine. Gymnosperms were the first seed plant on earth (meaning they appeared before angiosperms). **Most gymnosperms do not have flagellated sperm - the sperms are dispersed by wind. Seeds are their dispersal unit, and their dominant generation is sporophyte.

Plant Tissues → Dermal Tissue

Is found on the outer layer of the plant. It provides protection to the insides of the plant and also helps regulate how the plant is affected by its external environment. 1. Epidermis is a type of dermal tissue that covers the outside of a plant. The epidermis of the plant is covered by a waxy layer, known as the cuticle. The waxy cuticle "waterproofs" the plant (limits evaporation of water). This is especially found in plants found in hot climates as it helps them survive the high temperatures. Root hairs are little structures that project out of the epidermis of root cells. They increase the surface area of the epidermis cells which allow for greater water and nutrient uptake. Larger surface area means larger amount of space where the plant is in contact with and can draw substances from the soil.

Flower Structures: Stamen

Is the male plant sex organ. It is composed of an anther, and a filament that supports the anther. → The anther is the site of microspore formation. In the anther, meiosis of precursor cells generates microspores. → The microspore then undergoes mitosis to form two cells - a generative cell (which contains the male gamete, or sperm) and a tube cell (which eventually develops into the pollen tube). These two cells combined are the pollen.

Plant Hormone: Cytokinins

Like auxins, regulate cell differentiation and division. The ratio of auxin to cytokinin affects cell growth. Cytokinins can prevent senescence (aging) of plants.

What is the Steele? What is it composed of?

Phloem and xylem are arranged to form the stele, the central part of the root or stem. The stele is composed of xylem, phloem and supporting ground tissue (pith). Pith is the tissue found at the center of the root or stem. It is actually made of parenchyma tissue (which we just learned is a type of ground tissue). However it is functionally similar to vascular tissues in that it also stores and transports materials throughout the plant.

What kind of relationship do plants and nitrogen-fixing organisms have?

Plants and nitrogen-fixing organisms have a symbiotic (mutually beneficial) relationship. Plants give the bacteria carbohydrates produced from photosynthesis, while the bacteria "fix" the nitrogen in the soil into a form that the plants can use.

Describe the risks associated with plants closing and opening their stomata for too long

Plants minimize transpiration by closing their stomata and keeping water in. But when stomata are closed, the plants are keeping CO₂ out as much as they are keeping water in. CO₂ is necessary to carry out photosynthesis, and photosynthesis is the source of food for plants. If the stomata stay closed for too long, the plant will essentially starve. When plants open their stomata, CO₂ can enter into the leaves, and the plant can produce food via photosynthesis. But remember, if the stomata stay open for too long, the plant will dry up because of transpiration. Plants must be able to regulate the opening and closing of the stomata to achieve this tricky but necessary balance between the need for food and the need for water.

Plant Hormone: Auxins

Promote the growth of stems by loosening cellulose fibers, increasing cell wall plasticity and causing cell growth. These plant hormones function with cytokinins to promote cell differentiation and division Auxins are one of the main hormones responsible for plant tropisms - growth in a certain direction. The different types of tropisms are listed below. Auxin will concentrate on one side of the stem, and cause increased growth on this side. Stem growth will become asymmetric, and cause the stem to curve.

Plant Tissues → Vascular Tissue → Phloem

transports sugars that are created in the leaves via photosynthesis to other areas of the plant that need sugar but can't produce it. The primary target is the roots, where there is a high carbohydrate storage. · Source: leaves · Sink: roots Phloem is made up of two types of cells: 1. Sieve cells are long cells with pores that allow substances to flow through them. Sieve cells are connected together to form a sort of continuous tunnel through which substances flow. They lack organelles because they need to efficiently and quickly transport the sugars. 2. Companion cells: Because they lack organelles, sieve cells are connected to companion cells, which have all the necessary organelles to carry out metabolic functions (such as load the sieve cells with the sugars they need to transport). Sieve cells and companion cells are connected via plasmodesmata (small channels that connect adjacent cells' cytoplasm), which allows for quick communication between the two.

Plant Tissues → Vascular Tissue → Xylem

transports water taken in from soil by the plant at the roots and transported to other areas of the plant that need the water but do not have direct access to it. The primary target is the leaves. · Source: roots · Sink: leaves Xylem is made up of two types of cells: 1. Tracheids are long, thin, and organized so that they are in contact with other tracheid cells by overlapping their tapered ends. Water flows from tracheid to tracheid through pits found at these ends. 2. Vessel elements are shorter and stouter, and are in contact with other vessel elements. Water flows from vessel element to vessel element through perforations along their cell walls. Along with water conduction, both also provide structural support.

Primary growth

vertical growth of plant @ apical meristems

Leaf Structure: Stomata

· Along the lower epidermis are several small openings called stomata that allow for gas exchange between the external environment and the plant, and open and close depending on the situation.

Leaf Structure: Bundle Sheath cells

· Bundle sheath cells surround and protect vascular bundles and are important cells for C₄ plants. Vascular bundles is the system that transports materials such as water and sugars.

Homosporous v. Heterosporous Plants

· Homosporous plants only produce one type of spore, making it a bisexual gametophyte. · Heterosporous plants produce two types of spores, both male and female. → Microspores are male gametophytes. → Megaspores are female gametophytes. → TIP: Human eggs are larger (more mega) than human sperm (more micro). Megaspores are plant 'eggs' (female), microspores are plant 'sperm' (male).

Leaf Structure: Epidermal layer

· Leaves are covered by an epidermal layer, which is covered by a waxy layer, called the cuticle that "waterproofs" the plant.

Leaf Structure: Mesophyll

· Mesophyll - the middle part of leaf (between upper epidermis and lower epidermis). There are two types of mesophyll: →The palisade mesophyll are tightly-packed cells that carry out photosynthesis and are found closer to upper epidermis. You can remember this by thinking that both "palisade" and "photosynthesis" start with the letter P. →The spongy mesophyll are loosely-packed, allowing for a lot of space between the cells and is found closer to lower epidermis. The "sponginess" of the spongy mesophyll allow for gas exchange between the external environment and the leaf, explaining why the spongy mesophyll is found next to lower epidermis where stomata are located.

Nitrogen Cycle aka Nitrogen Fixation: Reservoir

· Nitrogen is essential for plant growth and development · The Earth's atmosphere = one of the reservoirs for nitrogen. · Nitrogen makes up around 78% of the Earth's atmosphere.

MOVEMENT OF FOOD: Pressure Flow Hypothesis

· Related to the source to sink theory is the pressure flow hypothesis. This hypothesis explains the movement of sugar in the phloem in relation to the movement of water. Source cells in the leaves produce sugar and load the sugar into the phloem at the leaves. · This increases the sugar concentration inside phloem cells, creating a gradient that pulls water (from the xylem which is nearby) into these phloem cells. This, in turn, creates a turgor pressure in the phloem, which results in a bulk flow movement of the sugar (and water) from the source (leaves) down to the sink (roots).

Tracheophytes → Seed-bearing → Angiosperms → Monocotyledons aka monocots

· Single cotyledon · Parallel leaf venation · Flower organs in multiples of 3's · Their vascular bundles are scattered Their root system is fibrous (many fine roots rather than a single large root)

Secondary growth → cork cambium

· The cork cambium is a ring of meristematic tissue located beyond the phloem, closer to the edge. Cells of the cork cambium repeatedly divide to form the cork. The cork is the outermost layer of the bark and serves as a protective layer for the plant. It protects the plant from various things, such as water loss, animals, insects, and other environmental stresses. · All plants undergo primary growth but only woody plants undergo secondary growth. Herbaceous (non-woody) plants do not exhibit significant secondary growth

Leaf Structure: Guard cells

· The opening and closing of the stomata are controlled by guard cells - specialized epidermal cells that surround the stomata

Tracheophytes → Seed-bearing → Angiosperms → Dicotyledon aka dicots

· Two cotyledons · Netted/branching leaf venation · Flower organs in multiples of 4's or 5's · Their vascular bundles are organized in a circle They have a taproot (a single large root)

Movement of Water: What direction does water move in? The main driving force behind this movement is...

· Xylem transports water from roots to leaves in one direction so it's unidirectional - it only goes up · The main driving force behind this movement is transpiration - when water evaporates out through stomata in the leaves (and partially in the stem). Transpiration causes transpirational pull. · Transpirational pull is a cohesive force. Cohesion is when similar particles or surfaces cling to one another, for example water molecules clinging together within a column of water. As water evaporates - because of cohesion - it pulls on the water column underneath it, and lifts the entire water column higher (bulk flow). This is known as the cohesion-tension theory, astension (pulling) is caused via cohesion.

Key Features of Bryophytes

· nonvascular plants EX: mosses, hornworts, and liverworts · most bryophytes do not have vascular tissue · do not have roots · This limitation forces bryophytes to be relatively simple → must remain small and short → grow horizontally so that everything can be near the water and nutrient source (think about a moss growing horizontally along a tree stump). · mostly found in moist habitats · contain rhizoids (hair-like projections) which aid in water absorption and provide minor anchorage. · spend most of their life cycle in the gametophyte stage. · possess flagellated sperm and use spores as their dispersal unit. · have a reduced sporophyte, which consists of a seta, foot, and sporangia. The sporophyte is usually dependent on and attached to the gametophyte for survival.

Nitrogen Cycle aka Nitrogen Fixation: Release Process

· plants and animals die and decay, known as detritus, which decomposes back into the soil to contribute a nitrogen source. · Any nitrates (NO₃⁻) not taken up by plant roots are released back into the atmosphere by denitrifying bacteria (release), when they convert nitrates (NO₃⁻) into N₂ atmospheric nitrogen.

Nitrogen Cycle aka Nitrogen Fixation: Assimilation

· plants can only use specific forms of nitrogen: ammonia and nitrate · they acquire the help of nitrogen-fixing organisms to convert nitrogen into these forms 1. Nitrogen fixing bacteria in the root nodules of legumes can fix atmospheric nitrogen (N₂) into ammonia (NH₃) and ammonium (NH₄⁺). 2. Nitrifying bacteria convert ammonia and ammonium into nitrites (NO₂⁻) and nitrites into nitrates (NO₃⁻). 3. Nitrates (NO₃⁻) are taken up by plants (assimilation of nitrogen), and the plants incorporate the nitrogen into amino acids and into chlorophyll *nitrogen utilized by consumers

Tracheophytes

· vascular plants · contain xylem and phloem vessels → effective means of transporting water and nutrients to different areas of the plant · grow vertically and tall (think of a tree). · have a root system which anchors them in place · spend most of their life cycle in the sporophyte stage. · There are two types of vascular plants: 1. Seedless tracheophytes 2. Seed-bearing tracheophytes