Biology Unit Review: Cell Structures, Division, and Systems

Foundations of Cell Biology

  • Definition of a Cell Organelle: A specialized structure within a cell.

  • Functions of Organelles: Organelles perform several vital roles, including:

    • Cellular respiration.

    • Creation of proteins, fats, and other components.

    • Recycling cell components.

  • Basic Unit of Life: The cell is the fundamental unit of all life.

Organelle Structures and Functions

  • Nucleus: Acts as the control center of the cell and contains the DNA.

  • Nucleolus: Located inside the nucleus; its primary function is to make ribosomes.

  • Ribosome: Responsible for making proteins.

  • Rough Endoplasmic Reticulum (Rough E.R.): Characterized by ribosomes attached to its surface to help make proteins.

  • Smooth Endoplasmic Reticulum (Smooth E.R.): Lacks ribosomes; responsible for making other molecules such as steroids and fats.

  • Mitochondria: Perform cellular respiration to provide energy to the cell.

  • Golgi Body: Sorts and packages molecules, such as proteins, to be transported.

  • Cytoplasm (or Cytosol): The fluid-like substance that contains and supports the organelles.

  • Cytoskeleton: Helps the cell maintain its structure.

  • Cell Membrane: Separates the internal environment of the cell from the outside environment.

  • Vacuole: Used for storage of food and water.

    • Central Vacuole: A very large vacuole found specifically in plant cells.

  • Cell Wall: A rigid structure located outside the cell membrane; it supports and protects the cell (found in plants only).

  • Chloroplasts: Perform photosynthesis in plant cells to produce glucose.

Cellular Processes: Diffusion, Osmosis, and Growth

  • Diffusion: The movement of particles of a substance from an area of high concentration to an area of low concentration.

  • Osmosis: The process when water diffuses through a semi-permeable membrane.

  • Resource Constraints on Cell Size: Cells cannot simply grow larger and larger indefinitely because as a cell increases in size, it takes longer for substances (like water) to cross the membrane via osmosis and then move (diffuse) across the cell to where they are needed. If the cell is too large, it will die before nutrients can reach their destination.

The Cell Cycle and Genetic Material

  • Importance of DNA: DNA is the genetic material that contains the information and instructions for the cell.

  • Stages of the Cell Cycle: The cell cycle is the continuous sequence of cell growth and division, consisting of two main stages:

    • Interphase: The growth stage where the cell spends about 90%90\% of its life.

    • Cell Division: The process where the cell divides its DNA and organelles to form two new identical cells.

Phases of Interphase

  • G1G_1 Phase: The first growth stage where the cell performs its normal functions in an organism.

  • SS Phase: DNA duplication (DNA replication) occurs.

  • G2G_2 Phase: The cell grows larger to prepare for cell division.

Cell Division and Mitosis

  • Mitosis: The division of the nucleus and its contents. It consists of four distinct phases:

    • Prophase: DNA condenses into visible chromosomes, the nuclear envelope breaks down, and spindle fibers form.

    • Metaphase: Chromosomes (condensed DNA) line up in the middle of the cell and attach to spindle fibers.

    • Anaphase: Spindle fibers pull the sister chromatids apart, pulling the two separated chromosomes to opposite ends (poles) of the cell.

    • Telophase: The nucleus begins to reform at each pole and DNA unwinds.

  • Cytokinesis: The division of the cytoplasm and organelles. This occurs differently based on cell type:

    • Animal Cells: The cell membrane pinches in to form a cleavage furrow.

    • Plant Cells: A cell plate forms to divide the cell.

  • Purposes of Cell Division: Cell division allows organisms to carry out growth, repair of tissues, and maintenance (replacing dead cells).

Tumors and Cancer

  • Tumor: An abnormal group of cells.

  • Formation: Tumors form when cells do not die but continue to divide and make more copies of themselves.

  • Cancer Causes: Cancer can be caused by mutations (mistakes) in DNA. For example, skin cancer can be caused by UV exposure. These mutations cause cells to undergo mitosis continuously without dying, along with their daughter cells, forming a tumor.

Cell Specialization and Plant Systems

  • Cell Specialization: The process where cells develop from similar cells into cells that have specific functions in a multicellular organism.

  • Differentiation: The series of events where an unspecialized cell develops into a specialized cell.

  • Tissues: Groups of similar cells that work together to perform a similar, specialized function.

  • Organs: Contain various tissues that work together to perform a specific function.

  • Organ Systems: Various organs that work together to complete a common task.

Plant Tissues and Their Functions

  • Dermal Tissue: Forms a protective barrier between the plant and the environment; protects inner tissues and controls gas exchange (including water vapor).

  • Vascular Tissue: Transports water and nutrients through the xylem and glucose through the phloem.

  • Ground Tissue: Performs various functions including photosynthesis and providing support.

Plant Organs and Their Functions

  • Roots: Take in water and nutrients from the soil.

  • Leaves: Provide a large surface area for photosynthesis.

  • Stem: Provides physical support for the plant and handles the transportation of water, nutrients, and glucose.

  • Flower: The reproductive organ of the plant.

  • Meristematic Cells: Unspecialized plant cells that can produce various specialized cells.

Animal Tissues and Human Organ Systems

Main Animal Tissues

  • Muscle: Allows body parts to move or change shape.

  • Epithelial: Covers the external and internal body surfaces.

  • Connective: Strengthens, supports, and connects various tissues.

  • Nervous: Senses and transmits information.

Human Organ Systems

  • Respiratory System: Responsible for gas exchange. All cells need oxygen (O2O_2); the respiratory system takes in oxygen from the air and removes carbon dioxide (CO2CO_2) at the alveoli of the lungs.

  • Digestive System: Responsible for the intake of food/nutrients and the removal of waste.

  • Circulatory System: Delivers nutrients and oxygen throughout the body and removes waste products.

  • Reproductive System: Contains reproductive organs used to produce offspring.

Cardiovascular and Respiratory Anatomy

  • The Heart: Pumps blood through the body. It is made of nervous, muscle, and connective tissues. Muscles provide the pressure, and nerves regulate the heartbeat by sending signals to the muscles to contract or expand.

  • Blood Vessels:

    • Arteries: Carry blood away from the heart.

    • Veins: Carry blood back to the heart.

    • Capillaries: The smallest blood vessels that connect arteries and veins; they are the site of gas and nutrient exchange.

  • Red Blood Cells: Carry oxygen and carbon dioxide throughout the circulatory system.

The Human Digestive System

  • Stages of Digestion: Ingestion, Digestion, Absorption, Elimination.

  • Path of Food: Mouth $\rightarrow$ Esophagus $\rightarrow$ Stomach $\rightarrow$ Small Intestine $\rightarrow$ Large Intestine $\rightarrow$ Rectum (storage) $\rightarrow$ Anus (exit).

  • Small Intestine: Site where the digestion of food is completed and absorption of nutrients begins. Nutrients are absorbed through structures called villi and microvilli.

  • Anus: Functions to eliminate undigested food in the form of feces from the body.

  • Additional Digestive Organs: Liver, Gallbladder, Pancreas.

Biotechnology and Ethics

  • GMOs (Genetically Modified Organisms): Organisms whose genetic material has been altered.

    • Pros: Crops can be made drought-resistant, yields can be increased, and medicines can be produced from other organisms.

    • Cons/Controversy: Long-term health effects of consumption are unknown; potential for cross-contamination of organic crops; concerns for people with allergies; difficulty in eliminating contamination.

  • Stem Cells: Unspecialized animal cells that can produce various specialized cells.

  • Stem Cell Research Controversy:

    • Pros: Could cure many diseases and allow for the growth of replacement organs.

    • Cons: Ethical debates occur because some stem cells come from embryos (considered taking a life by some). Other stem cells are made from skin cells using viruses, which could potentially damage the cells. The debate centers on the ethics of life versus medical applications.

  • Difference in Unspecialized Cells: Meristematic cells refer to plants, while stem cells refer to animals.