Plant half exam one (ex 4)

Ways plant mediate climate change.

• Removing CO 2 from the atmosphere

• Adding water vapor to the atmosphere

• Changing the albedo (how reflective Earth’s surface is)

helping with water run off and erotion

Three plant cell tyes

1) Parenchyma

2) Collenchyma

3) Sclerenchyma

What are the differences between primary and secondary cell walls?

Primary cell walls are not as strong as they are not relied on for structure as much but secondary cell walls are dead once they become a true secondary cell wall. Secondary wall is linned with lignin to make it stronger.

Define both primary and secondary growth.

Primary Growth

• Goal: Lengthens shoots and roots so plants can reach sunlight and absorb water/minerals.

• Location: Driven by apical meristems located at the tips of roots and shoots (as well as intercalary meristems in grasses).

• Process: Involves cell division, cell elongation, and differentiation into primary tissues (protoderm, ground meristem, and procambium).

Secondary Growth

• Goal: Increases the diameter, width, and structural support of woody stems and roots.

• Location: Driven by lateral meristems—specifically the vascular cambium and cork cambium

• Process:

  • The vascular cambium divides to produce secondary xylem (lignified wood) inward and secondary phloem outward.

  • The cork cambium produces tough, water-repelling cork cells and phelloderm, which combine to form the protective periderm (bark).

3 Tissue systems

• Dermal: covers/protects outside of

plant, manages gas exchange and

water loss

• Vascular: transports water, minerals

and sugars through the plant

• Ground: bulk of plant interior; lots of

functions (photosynthesis, food/water

storage, structural support)

Parenchyma

Parenchyma cells only have primary cell wall living cells

Thin, relatively even thickness to cell wall

Parenchyma cells perform a wide variety of tasks

Found in every plant organ. photosynthesis and

metabolism,

– storage, secretion and

transport of sugars

– Wound repair

– form adventitious roots

Sclerenchyma cells have secondary cell wall dead cells

lignified, extremely rigid

provide structural support and important role in

conducting water throughout plant

Collenchyma

Collenchyma cells only have primary cell wall living cells

uneven thickening of primary cell wall

Occur in leaves, stems, not common in roots

Primary function is support for young, growing tissues

Provide flexible support and strength to young growing tissues

Sclerenchyma

Sclerenchyma cells have secondary cell wall dead cells lignified, extremely rigid provide structural support and important role in conducting water throughout plant.

strength, support, water transport.

indeterminate growth

1. Plants grow by adding parts rather than by increasing size of

existing parts

2. Some regions of the plant are partially independent

- mutations localized; allow for continuous growth.

3. Flowers and gametes are produced at many locations – not

just in one set of reproductive cells

4. Plant can constantly adjust to environmental conditions

meristems

Apical meristems

• located at the tips of roots and

shoots elongation

Lateral meristems

• located in stems and roots allow

plants to grow in circumference

• Woody plants only

vascular cambium

lateral meristem - a tissue made of actively dividing, unspecialized stem cells responsible for secondary growth in the stems and roots of dicots, gymnosperms, and many other vascular plants.

Differences in Cell Division

Periclinal Division:

• Plane: Occurs parallel to the adjacent surface or tissue layer.

• Outcome: Produces a new layer of cells stacked internally or externally, which increases the thickness, depth, or number of layers in the tissue.

Anticlinal Division:

• Plane: Occurs perpendicular (at a right angle) to the adjacent surface or circumference.

• Outcome: Increases the surface area and circumference of a cell layer by adding more cells side-by-side.

Palisade Mesophyll (Light Acquisition)

• Column-Shaped Orientation: Cells are elongated and arranged vertically (perpendicular to the leaf surface) like columns. This shape increases the surface area of cell membranes facing the light and allows light to penetrate deeper into the leaf rather than being absorbed all at once in the top layer.

• High Chloroplast Density: Packed densely beneath the transparent upper epidermis, palisade cells house the majority of the leaf's chloroplasts to maximize light absorption for photosynthesis.

Spongy Mesophyll (Acquisition and Internal Circulation)

• Loose Arrangement and Air Spaces: Located below the palisade layer, spongy mesophyll cells are irregularly shaped and loosely packed.

• Intercellular Air Network: Up to 50% (or more) of this layer consists of large intercellular air spaces. This forms a continuous internal gas-exchange network that allows CO2 to diffuse rapidly and reach every photosynthetic cell inside the leaf interior.

Stomates (Gas Entry and Regulation)

• Pores for Gas Exchange: Stomata are microscopic openings—mostly located on the lower epidermis—that let atmospheric co2 diffuse into the leaf's internal air spaces.

• Guard Cell Control: Each stoma is flanked by two guard cells that change shape based on turgor pressure. They open when the plant has enough water to let co2 in, and close when water is scarce or in the dark to limit water loss via transpiration.

Vascular Bundles (Support and Resource Transport)

• Xylem Hydration: Vascular bundles (veins) run directly through the mesophyll, using the xylem to deliver water and dissolved minerals absorbed by the roots up to the photosynthetic cells. Water is essential for splitting molecules during photosynthesis and maintaining the cell turgor pressure that keeps stomata functional.

• Phloem Export: The phloem simultaneously transports the sugars produced in the mesophyll away to other parts of the plant, preventing product buildup and maintaining metabolic efficiency.

carbon balancing

Photosynthesis (Carbon Gain) and Respiration (Carbon Loss)

• A positive carbon balance leaves a surplus of sugars and carbon skeletons, which the plant uses to build new leaves, stems, roots, and flowers.

• Excess carbon is stored as starches or other reserves to help the plant survive periods of low light, winter, or stress.

• Without a sustained positive carbon balance over time, a plant cannot grow, reproduce, or maintain its existing tissues, eventually leading to starvation and death.

inputs and outputs of the light-dependent reactions

take place in the thylakoid membranes of chloroplasts

Inputs (Reactants)

• Light Energy (sunlight absorbed by chlorophyll)

• Water (split via photolysis)

• NADP+(nicotinamide adenine dinucleotide phosphate)

• ADP+ P (adenosine diphosphate plus inorganic phosphate)

Outputs (Products)

• ATP(adenosine triphosphate, chemical energy for the Calvin cycle)

• NADPH (high-energy electron carrier used in the Calvin cycle)

• Oxygen (released into the atmosphere as a byproduct)

Thylakoid

• A membrane-bound, flattened, disc-like sac located inside the chloroplast.

• Function: It contains chlorophyll and other light-absorbing pigments.

Grana

• A stack of multiple disk-shaped thylakoids piled on top of each other, resembling a stack of coins.

• Stacking thylakoids into grana greatly increases the surface area available for trapping light energy, making photosynthesis much more efficient.

Photophosphorylation

where ADP (adenosine diphosphate) combines with an inorganic phosphate to form ATP (adenosine triphosphate)