Plant Classification, Structure, and Ecology
Plant Classification
Plants are classified into three main groups:
- Bryophyta (mosses and liverworts): These inhabit moist environments and depend on water for reproduction. They do not produce flowers or seeds.
- Pteridophyta (ferns and horsetails): These have independent vessels for water transport. Their leaves and roots, known as fronds, contain spores involved in asexual reproduction. They do not produce fruits or seeds.
- Spermatophyta (seed-producing plants): This group includes all flowering plants and seed-producing plants like trees, shrubs, and herbs. Gymnosperms, the older spermatophytes, have exposed seeds (e.g., evergreens) and typically rely on wind pollination (anemophily). Angiosperms, their successors, have seeds enclosed within fruits. Angiosperms are further divided into monocots (one cotyledon) and dicots (two cotyledons).
Fungi
Fungi are chemoheterotrophic organisms. They have eukaryotic cells, are aerobic, and may perform external digestion. They can be unicellular or multicellular. Multicellular fungi are called mycelia, which consist of branched filaments known as hyphae. Many fungi exhibit saprophytism, parasitism, or symbiosis. They are not classified within the plant kingdom because they are chemoheterotrophic, while plants are photoautotrophic. All plants have diplohaplontic life cycles with an alternation of generations.
- In Bryophyta, the gametophyte is the dominant phase (e.g., moss), and the sporophyte appears under suitable conditions. Meiosis occurs within the sporophyte, producing meiospores (n) that germinate to produce the gametophyte (n). The gametophyte forms gametes (n) that fuse to form the sporophyte (2n).
- In Pteridophyta, the gametophyte is less prominent, while the sporophyte is the dominant phase. The sporophyte (2n) produces meiospores (n) that germinate to produce the gametophyte (n). The gametophyte contains reproductive organs that produce gametes (n), which fuse to form the sporophyte (2n).
- In Spermatophyta, the sporophyte plant is the dominant phase, and the gametophyte is less visible. The sporophyte (2n) produces reproductive structures called flowers. Flowers produce two types of meiospores, male (n) and female (n), which develop into male (n) and female (n) gametophytes, respectively. These gametophytes produce gametes (n) that fuse to form a sporophyte (2n).
Plant Communities
A community is a set of populations living in one place. A plant community is a collection of plants from different species. The main types of plant communities are:
- Forest: Dominated by trees.
- Maquis: Dense shrubland (1.5-3 meters high).
- Weed: Low shrubland (0.5-1 meter high) with clearings.
- Meadows: Dominated by herbaceous plants.
Vegetation Layers
Vegetation layers are different levels within a plant community’s structure. Common layers include:
- Tree layer: Dominant trees with an understory (e.g., oak).
- Shrub layer: Shrubs, saplings, and climbing plants (e.g., honeysuckle, laurustinus, buckthorn).
- Herbaceous layer: Herbaceous plants (e.g., false brome, wild madder).
- Muscinal layer: Mosses, lichens, and herbs.
Sunny, south-facing slopes receive more solar radiation, have less moisture, and lower productivity. Shaded, north-facing slopes receive less solar radiation, are wetter, and have higher productivity. The ecological matrix comprises environmental variables (e.g., moisture, light).
Plant Processes
Photosynthesis is the process of plant nutrition.
Osmosis is the process where water moves across a semipermeable membrane from a less concentrated (hypotonic) solution to a more concentrated (hypertonic) solution.
Diffusion is the movement of molecules and ions from an area of higher concentration to an area of lower concentration, following a concentration gradient.
Photosynthesis is an anabolic process that produces organic matter from inorganic matter. Light energy is stored in chemical bonds. It consists of two phases:
- Light-dependent phase: Photolysis of water occurs, producing energy.
- Light-independent phase (dark phase): CO2 is converted into organic matter.
The main function of photosynthesis is to obtain organic matter.
Plant Cell Structure
Plant cells are eukaryotic cells characterized by:
- Cell wall: Thick and rigid outer layer.
- Cell membrane.
- Cytoplasm: Cytoskeleton, Golgi complex, endoplasmic reticulum.
- Chloroplasts: Involved in photosynthesis (give plants their green color).
- Parenchyma cells: Contain chloroplasts.
- Mitochondria, ribosomes, and vacuoles.
Autotroph: An organism or cell that transforms inorganic carbon into energy.
Saprophage: An organism that feeds on decomposing organic matter (e.g., rotting wood).
Coprophage: An organism that feeds on excrement.
Detritivore: An organism that feeds on organic matter, either plant or animal.
Plant Adaptations and Ecology
Tropisms are directional growth responses of plants to stimuli. Types of tropisms include:
- Phototropism: Response to light.
- Thigmotropism: Response to touch.
Macrophytes: Phytoplankton, the primary entry point for matter and energy in aquatic ecosystems.
Hygrophilous plants: Plants with roots near the soil surface, requiring abundant water and humidity.
Hydrophytes: Plants that can have roots and leaves submerged or floating on the surface.
Algae Groups
Algae groups include:
- Chlorophytes (green algae).
- Rhodophytes (red algae).
- Phaeophytes (brown algae).
Independent variable: The variable that is changed.
Dependent variable: The variable that is measured or observed.
Spermatophyte Body
The body of a spermatophyte consists of a vegetative apparatus and a reproductive system.
Characteristics of Climbing Plants
Climbing plants have adaptations such as:
- Caulogenic roots.
- Rigid spines and thorns.
- Tendrils for attachment.
- Twining stems (voluble plants).
Ecosystems and the Ecosphere
Ecosystem: A group formed by a community of organisms (biocenosis) and their physical and chemical environment (biotope), including light, temperature, and availability of liquid water.
Ecosphere: The region of space encompassing Earth, extending from the subsurface to the upper atmosphere, and potentially including parts of Mars and Jupiter, where life can exist. Life on planets requires CHON (carbon, hydrogen, oxygen, nitrogen), water, an energy source, a magnetic field, and gravity.
Chemosynthesis: Energy production using chemical compounds (e.g., sulfides).
Photoheterotrophic photosynthesis: Performed by certain bacteria.
Photoautotrophs: Plants.
Chemoheterotrophs: Animals (e.g., humans).
Chemoautotrophs: Certain bacteria.
Mutualism: An interspecific relationship where both organisms benefit.
Symbiosis: An interspecific relationship, such as in lichens.
Competition: Interspecific and intraspecific competition for resources.
Parasitism: An interspecific relationship where one organism (the parasite) benefits at the expense of another (the host).
Predation: An interaction where one organism (the predator) kills and consumes another (the prey).
Commensalism: An interaction where one organism benefits, and the other is neither harmed nor helped.
Inquilinism: An interaction where one organism uses another for protection.