Biological Concepts: Cells, Classification, and Plant Structure
The Biosphere and Characteristics of Life
The biosphere is the layer of Earth where living beings exist, encompassing land and aquatic habitats. It is not continuous, making its limits difficult to specify, yet it exhibits both diversity and uniformity.
Features of Living Beings
Living beings are characterized by the following:
- They are made of biomolecules.
- They are highly organized structures.
- They perform vital functions (reproduction, nutrition, and relationship/response to stimuli).
Molecular Composition
Organic Molecules: These are exclusive energy sources and storage units.
Inorganic Molecules: These are found in the physical environment and do not provide energy.
Vital Functions
Nutrition
Living beings exchange matter and energy with their environment. Nutrition can be:
- Autotrophic: Organisms make their own food.
- Heterotrophic: Organisms take nourishment from their environment.
Relationship (Interaction)
This is the process of reactions between living beings and their environment or other organisms. Organisms relate to their environment and respond to stimuli.
Reproduction
This is the process by which living beings produce offspring.
- Sexual Reproduction: Involves two parents (often with distinct genders) and the formation of gametes.
- Asexual Reproduction: Involves only one parent.
Cellular Biology
The Cell: Basic Unit of Life
The cell is the basic functional unit of all living beings, performing vital functions. It cannot be seen with the naked eye. Living beings (organisms) can be unicellular or multicellular.
Prokaryotes vs. Eukaryotes
Prokaryotes: These are primitive cells lacking membrane-bound organelles. Their genetic material is dissolved in the cytoplasm, and they lack a true nucleus.
Eukaryotes: These are evolved cells that are compartmentalized and possess a true nucleus.
Key Organelles
Chloroplast
The site of photosynthesis. It has an inner and outer membrane filled with stroma. Inside the inner membrane, there is a stack of sac-like structures called grana (typically 5 or 6 sacs).
Vacuole
A membrane-bound organelle that stores reserve substances.
- In animal cells, vacuoles are small and numerous.
- In plant cells, they are typically large and singular.
Classification and Kingdoms
Taxonomy and Species
Taxonomy: The science responsible for classifying living species.
Species: The smallest taxonomic category, defined by individuals that can interbreed and produce fertile offspring.
Five Kingdoms of Life
The five recognized kingdoms are:
- Monera (Bacteria)
- Protoctista (Protists)
- Fungi
- Plantae (Plants)
- Animalia (Animals)
The Monerans
This kingdom is composed of simple, single-celled organisms, including bacteria and cyanobacteria.
Plant Biology Examples
Plant Divisions
Gymnosperms: These are vascular plants that produce seeds, often having cones or simple flowers, but lacking true fruit.
Angiosperms: These are vascular plants that produce flowers and true fruits.
Flower and Stem Structure
Parts of the Flower
The main components include the calyx, corolla, gynoecium, pistil, anther, petal, sepal, ovary, and peduncle.
Stem Structure
Key structures include the bud, leaf, internode, branch, main stem, and nodes.
Fruit Development
Fruit Formation: After fertilization, the calyx and corolla wilt. The ovary then grows, increases in mass, and eventually matures into the fruit.