Plant Structures and Their Functions

Study Notes

Plants and algae are the primary producers in food webs and food chains, synthesizing food from sunlight through photosynthesis.
Photosynthesis is an endothermic reaction, absorbing more energy than it releases, with the overall equation: carbon dioxide + water → glucose + oxygen
Factors affecting the rate of photosynthesis include:
- Temperature: Enzymes control the reaction; increasing temperature boosts the rate until enzymes denature, decreasing the rate.
- Light Intensity: Higher light intensity generally leads to a faster rate; photons (light energy) hitting chloroplasts increase reaction rate.
- Carbon Dioxide Concentration: A higher concentration increases the rate; more CO2 is needed for glucose production.
Any factor can become limiting: Even if other factors increase, the rate can't increase past the limit imposed by the limiting factor. This is evident on a graph by the curve flattening.
A single-factor graph shows the limiting factor's effect on the rate, with the limiting factor on the x-axis and the reaction rate on the y-axis; multiple-factor graphs display multiple lines corresponding to different environmental conditions.

Design an experiment measuring a plant's oxygen production (rate of photosynthesis) using pondweed, a water bath, capillary tube, syringe, lamp, and ruler.
The independent variable should be the distance of the lamp from the pondweed, while other variables (e.g., temperature, exposure time) are controlled.

Light intensity is inversely proportional to the distance squared from the light source (inverse square law): Light intensity = 1/distance².

Root hair cells: Specialized for water and mineral ion uptake, showing a large surface area for increased absorption and a large central vacuole, with mitochondria for energy.
Xylem: Dead, lignified cells forming tubes for water transport; lignin provides support against pressure.
Phloem: Living cells with sieve plates for transport of sugars (sucrose). Energy for this is provided by mitochondria in companion cells.

Transpiration is water loss from leaves.
Stomata (pores) allow for gaseous exchange.
Guard cells regulate stomata opening and closing, influenced by water levels and light availability.

Translocation is the movement of sugars (e.g., sucrose) through the phloem from source (where they are made) to sinks (where they are stored or used).
Sources and sinks fluctuate depending on the time of year (e.g., roots in spring, leaves in summer).

Factors affecting transpiration rate include temperature, humidity, wind speed, and light intensity.

Plants in harsh environments (e.g., deserts) may have fewer leaves, modified leaf shape, and/or thick cuticles to minimize water loss.

Hormones like auxins regulate plant growth and responses.
Auxins: Stimulate cell elongation, influencing responses like phototropism (growth towards light) and gravitropism (growth responding to gravity).
Gibberellins: Involved in germination, stem elongation, and fruit development.
Ethene: Stimulates fruit ripening.