Cell Biology: Membranes, Photosynthesis, Reproduction, and More
Transport Across the Plasma Membrane
The plasma membrane selectively allows certain substances to pass through, depending on their size. Transport occurs through several mechanisms:
- Diffusion: Movement of substances from an area of high concentration to an area of low concentration across a permeable membrane.
- Osmosis: Movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
- Active Transport: Molecules are transported from an area of low concentration to an area of high concentration, requiring energy.
- Endocytosis/Exocytosis: Larger particles, like bacteria, are transported across the membrane via vesicles. Endocytosis brings particles into the cell, while exocytosis releases them.
Photosynthesis
Photosynthesis is the process of converting light energy into chemical energy in the form of organic matter. This process uses chlorophyll, the pigment that gives plants their green color. Photosynthesis occurs in two phases:
- Light-dependent reactions: Light energy splits water molecules. This occurs in the thylakoid membranes.
- Light-independent reactions (Calvin cycle): Occurs in the stroma and does not require light.
Bacteria
Bacteria are microscopic organisms that come in various shapes:
- Cocci: Round
- Bacilli: Rod-shaped
- Spirilla: Spiral
Bacteria are prokaryotic cells, lacking a nucleus and other membrane-bound organelles like mitochondria and the Golgi apparatus. Most bacteria are heterotrophic, but some are autotrophic, performing photosynthesis or chemosynthesis. Some bacteria are parasitic and cause disease, while others are beneficial symbionts.
The Cell Cycle
The cell cycle is the series of events that lead to cell division. It consists of two main stages:
- Interphase: The period between two consecutive cell divisions.
- Mitosis (cell division): The process of cell multiplication.
Asexual Reproduction
Asexual reproduction produces offspring that are genetically identical to the parent. Types of asexual reproduction include:
- Binary fission: A single cell divides into two identical daughter cells.
- Budding: A new organism develops from an outgrowth or bud due to cell division at one particular site.
- Regeneration: The ability to regrow lost or damaged body parts.
- Fragmentation: The body breaks into two or more pieces, each of which develops into a complete organism.
- Sporulation: Formation of spores.
Sexual Reproduction
Sexual reproduction involves the combination of genetic material from two parents, resulting in genetically unique offspring. Most multicellular organisms reproduce sexually. Types of sexual reproduction include:
- Isogamy: Gametes are morphologically identical.
- Anisogamy: Gametes are morphologically different (e.g., sperm and egg).
Unisexual species: Individuals are either male or female.
Hermaphroditic species: Individuals have both male and female reproductive organs.
Fertilization
Fertilization is the fusion of gametes to form a zygote.
- External fertilization: Common in aquatic animals; eggs and sperm are released into the water.
- Internal fertilization: Common in terrestrial animals; sperm are deposited inside the female’s body.
Reproductive Strategies
- Oviparous: Eggs are laid and develop outside the mother’s body.
- Ovoviviparous: Eggs are retained within the mother’s body until they hatch.
- Viviparous: The embryo develops inside the mother’s body, receiving nourishment through a placenta.
Blood
Blood is a liquid tissue composed of plasma (liquid containing water and dissolved substances) and formed elements:
- Red blood cells: Carry oxygen.
- White blood cells: Involved in immune defense.
- Platelets: Involved in blood clotting.
Cell Theory
The cell theory states:
- The cell is the basic structural and functional unit of life.
- All living organisms are composed of one or more cells.
- All cells arise from pre-existing cells.
Bioelements and Water
Bioelements are the chemical elements essential for life (e.g., carbon, hydrogen, oxygen, nitrogen). Water makes up about 70% of the human body and plays a vital role in life processes. Minerals also play an important role, especially in plants.
Anaerobic Respiration
Anaerobic respiration occurs in the absence of oxygen (e.g., fermentation).
Digestion
Digestion is the process of breaking down food into simpler molecules that can be absorbed by the body. It involves:
- Ingestion: Intake of food.
- Digestion: Breakdown of food into smaller molecules.
- Absorption: Uptake of nutrients into the circulatory system.
- Egestion: Elimination of undigested waste.
Vertebrate Digestive System
The vertebrate digestive system consists of the mouth, pharynx, esophagus, stomach, and intestines, along with accessory glands like the salivary glands, liver, and pancreas.
Respiration
Respiration is the process by which nutrients are oxidized in cells to produce energy. It involves an exchange of gases.
Nervous and Endocrine Systems
Animals have two systems for regulating and coordinating functions: the nervous system and the endocrine (hormonal) system. Plants only have a hormonal system.
Vertebrate Nervous System
The vertebrate nervous system is divided into:
- Central Nervous System (CNS): Brain and spinal cord.
- Peripheral Nervous System (PNS): Nerves and ganglia.
The CNS is protected by the skull and vertebrae, as well as by membranes called meninges.
Brain
The brain is composed of the cerebrum, cerebellum, and brainstem.
- Cerebrum: Responsible for higher-level functions like consciousness and thought.
- Cerebellum: Coordinates movement and balance.
- Brainstem: Controls basic life functions like breathing and heart rate.
Spinal Cord
The spinal cord transmits nerve impulses between the brain and the rest of the body.