Plant Structure, Function, and Reproduction; Animal Organization and Homeostasis – Study Guide

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Plant Structure and Growth

Plant Organs and Tissues

Plants are composed of three main organs: roots, stems, and leaves. These organs are made up of tissues, which are integrated groups of cells with a common structure and function. An organ is a specialized center of body function composed of several different types of tissues.

Roots: Anchor the plant, absorb minerals and water, and store carbohydrates.
Stems: Support leaves and transport fluids between roots and leaves.
Leaves: Primary site of photosynthesis, gas exchange, transpiration, and regulation of water loss.

Root Structure and Function

Roots serve to anchor the plant, absorb minerals and water, and often store carbohydrates. Root hairs increase the surface area for water absorption.

Leaf Functions

Photosynthesis: Conversion of light energy to chemical energy.
Gas Exchange: CO2 enters and O2 exits through stomata.
Transpiration: Water evaporates from leaf stomata, pulling water up from roots.
Regulation of Water Loss: Stomata open and close to balance CO2 uptake and water conservation.

Vascular Tissues

Xylem: Conducts water and dissolved minerals upward from roots.
Phloem: Transports sugars from leaves to other parts of the plant.

Growth and Meristems

Apical Meristems: Enable primary growth (lengthening).
Lateral Meristems: Enable secondary growth (thickening).

Dendrochronology and Growth Rings

Growth rings are formed by differential growth during the growing season. Early wood has large, thin-walled cells; late wood has thick-walled cells. Rings are absent in tropical trees due to lack of seasonal growth.

Root Adaptations

Prop-roots and Buttress Roots: Provide additional support in shallow soils.
Exposed Roots in Mangroves: Allow oxygen uptake in waterlogged soils.

Stomata and Guard Cells

Stomata are pores surrounded by guard cells, which regulate gas exchange and water loss.

Common Garden Experiments

Used to distinguish genetic vs. environmental influences on plant traits.

Secondary Growth and Cambium

Vascular Cambium: Produces secondary xylem and phloem.
Cork Cambium: Produces protective outer covering.

Labeled cross-section of tree stem showing periderm, phloem, vascular cambium, secondary xylem, primary xylem, and pith

Resource Acquisition, Transport, and Nutrition in Plants

Water and Nutrient Uptake

Plants acquire resources through specialized structures and processes. Mosses lack roots and absorb water and nutrients by diffusion and osmosis.

Overview of Resource Acquisition

CO2 uptake and O2 release through stomata.
Transpiration creates a pull for xylem sap.
Phloem sap moves sugars between sources and sinks.

Diagram of water potential gradient in a tree, showing root uptake, xylem cohesion and adhesion, and leaf evaporation

Apoplastic and Symplastic Routes

Water and minerals move through roots via apoplastic (cell wall) and symplastic (cytoplasm) routes. The Casparian strip in the endodermis regulates entry into the vascular cylinder.

Water Potential

Definition: Predicts the direction of water movement, influenced by solute concentration and pressure.
Water moves from regions of higher to lower water potential.
Adding solutes lowers water potential (always negative).

Unusual Nutritional Adaptations

Epiphytes: Grow on other plants, gather their own nutrients.
Parasitic Plants: Absorb nutrients from hosts.
Carnivorous Plants: Supplement diet by capturing insects.

Cohesion-Tension Hypothesis

Transpiration pulls water up the xylem, with cohesion and adhesion maintaining an unbroken chain of water molecules.

Diagram showing water movement in xylem via cohesion and adhesion

Stomatal Regulation

Guard cells control stomatal opening and closing.
Environmental stimuli: light, CO2 depletion, drought (abscisic acid).

Cation Exchange in Soil

Roots acidify soil, releasing H+ ions that displace mineral cations for uptake.

Translocation and Phloem Transport

Translocation: Movement of photosynthetic products in phloem.
Sugar Source: Net producer (e.g., mature leaf).
Sugar Sink: Net consumer (e.g., root, fruit).

Nitrogen Cycle and Mutualisms

Rhizobium: Nitrogen-fixing bacteria in legume root nodules.
Mycorrhizae: Fungi aiding nutrient and water uptake.

Angiosperm Reproduction and Double Fertilization

Flower Structure and Function

Flowers contain reproductive organs: stamen (male) and carpel (female). Essential parts for reproduction are the stamen and carpel.

Diagram of flower structure with labeled parts

Pollination and Fertilization

Pollination: Transfer of pollen to stigma.
Fertilization: Fusion of gametes to form zygote.
Double fertilization: One sperm fertilizes egg (zygote), other fertilizes two polar nuclei (endosperm).

Diagram showing pollen tube growth and double fertilization in ovule

Alternation of Generations

Plants alternate between haploid gametophyte and diploid sporophyte generations.

Diagram of alternation of generations in plants

Plant Response to Environmental Stimuli

Hormones and Tropisms

Auxins: Cell elongation, phototropism.
Gibberellins, Cytokinins, Abscisic Acid, Ethylene: Growth, dormancy, ripening, stress responses.
Tropisms: Phototropism (light), gravitropism (gravity), thigmotropism (touch).

Darwin and Darwin phototropism experiment Boysen-Jensen phototropism experiment