Chapter 2 - Cell Structure and Organization

Cell Structure

• Cells: Basic unit of life with organized structure for vital functions.

• Prokaryotic Cells: Simple, single-celled organisms without a nucleus, such as bacteria.

• Eukaryotic Cells: More complex cells that contain a nucleus and organelles, including plant and animal cells.

Cell Theory

1. All living organisms are composed of one or more cells.

2. The cell is the basic unit of structure, function, and organization in all organisms.

3. All cells come from pre-existing cells.

Types of Cells

• Prokaryotic:

  • Dispersed genetic material within cytoplasm, no defined nucleus and other membrane-bound organelles. (Bacteria and Archaea)

  • Reproduce through binary fission, allowing for rapid population growth under favorable conditions.

  • Possess a cell wall (usually made of peptidoglycan in bacteria).

  • Reproduce via binary fission.

  • Exhibit diverse metabolic pathways, enabling adaptation to various environments.

• Eukaryotic:

  • Defined nucleus enclosed within a nuclear organelles.

  • Protists, Fungi, Plants, and Animals

  • Have various organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, etc.

  • Reproduce via mitosis and meiosis.

• Plant:

  • Eukaryotic cells with a cellulose cell wall, chloroplasts for photosynthesis, and large central vacuoles for storage and support

• Fungi:

  • Eukaryotic cells with chitin cell walls, lacking chloroplasts, and typically decomposers in ecosystems.

• Animals:

  • Eukaryotic cells with no cell wall, flexible membranes, and specialized structures for diverse functions and tissues.

  • May have flagella for mobility

• Protist:

  • Eukaryotic microorganisms; some possess cell walls, but they lack differentiated tissues found in plants and animals.

  • May have cell wall, no differentiated tissues.

• Fungal:

  • Eukaryotic heterotrophs with a chitin cell wall; obtain nutrients by absorption.

Plant vs Animal:

Animal Cells:

• Cell membrane: Encloses the cell, regulating the passage of substances.

• Cytoplasm: Gel-like matrix containing organelles and facilitating biochemical reactions.

• Nucleus: Contains DNA and controls gene expression.

• Irregular shape due to the absence of a rigid cell wall.

• Glycogen granules store food in the cytoplasm.

• Small, temporary vacuoles primarily involved in digestion and excretion.

Plant Cells:

• Cell membrane: Encloses the cell and regulates molecular transport.

• Cytoplasm: Provides a medium for biochemical reactions; contains organelles.

• Nucleus: Controls cellular activities through gene expression.

• Cell Wall: Rigid outer layer made of cellulose; provides structural support and protection.

• Chloroplasts: Site of photosynthesis where solar energy is converted to chemical energy.

• Regular, rigid shape maintained by the cell wall.

• Starch grains store excess glucose produced during photosynthesis.

• Large, permanent vacuoles maintain cell turgor pressure and store water, nutrients, and waste.

• Mitochondria: Often referred to as the powerhouse of the cell, where energy is produced through respiration.

Cell Components

• Cell membrane: Outer boundary controlling substance passage.

• Cytoplasm: Gel-like matrix for biochemical reactions.

• Cell wall (in plants): Provides structure and support.

• Chloroplasts (in plants): Conducts photosynthesis.

• Nucleus: Contains DNA(genetic material) and controls cell activities.

• Endoplasmic Reticulum: Responsible for the synthesis of proteins (rough ER) and lipids (smooth ER), and plays a key role in transporting these materials throughout the cell.

• Vacuole: Stores water, nutrients, and waste; maintains turgor pressure.

• Mitochondria: Known as the powerhouse of the cell, they generate ATP through cellular respiration, providing the energy necessary for cellular functions.

• Ribosomes: Sites of protein synthesis, either free-floating in the cytoplasm or attached to the endoplasmic reticulum.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contains digestive enzymes that break down waste materials and cellular debris, acting as the cell's waste disposal system.

Cell Membrane

• Selective barrier regulating substance passage into and out of the cell.

• Specialized proteins for molecular transport and communication.

• Composed of a phospholipid bilayer with embedded proteins and carbohydrates.

Membrane Proteins

• Integral proteins: Embedded within the lipid bilayer.

• Peripheral proteins: Associated with the membrane surface.

Nucleus

• Houses DNA, controls gene expression and replication.

• Located in the center of eukaryotic cells.

Nuclear Envelope

• A double membrane that encloses the nucleus, separating it from the cytoplasm.

Cytoplasm

• Gel-like matrix within the cell for biochemical reactions, energy production, and transport.

• Provides structural support and suspends organelles.

Ribosome

• Synthesizes proteins based on genetic instructions encoded in mRNA.

• Located in cytoplasm (free ribosomes) and rough endoplasmic reticulum (bound reticulum).

Mitochondria

• Energy generation through cellular respiration (ATP production: adenosine triphosphate).

Cristae

• Inner membrane folds that increase surface area for ATP synthesis.

Vacuoles

• Store nutrients, water, ions, and waste products.

• Regulate turgor pressure in plant cells, maintaining cell rigidity and osmotic balance.

• May contain pigments for pollinator attraction.

Chloroplasts

• Site of Photosynthesis: solar energy into chemical energy.

• Produce glucose and oxygen from carbon dioxide and water.

Cell Wall

• Provides structure and support.

• Prevents bursting by becoming turgid.

Organisation of Living Organisms

• Organelles → Tissue → Organ → Organ system → Organism

  • Organelles are specialized subunits within a cell that perform specific functions.

  • Tissues are groups of similar cells performing specific functions.

  • Organs are structures composed of different tissues working together to perform a specific task.

  • Organ systems consist of multiple organs that cooperate to carry out complex functions.

  • Organisms are individual living entities composed of one or more organ systems.

Specialized Cells

• Animal Cells:

  • Red blood cell:

    • Oxygen transport from lungs to tissues, contain haemoglobin.

    • No nucleus: more space for oxygen

    • A biconcave shape to increase the surface area, allowing for rapid diffusion

    • Thin cell membranes to decrease the diffusion distance.

  • Neuron: transmits electrical signals throughout the body, composed of dendrites, an axon, and synapses

  • Epithelial cell: forms protective layers on surfaces, involved in absorption and secretion, characterized by tightly packed cells that create barriers.

  • Ciliated cell: Transports mucus and trapped particles in the respiratory tract.

  • Motor nerve cell: transmits electrical impulses to coordinate muscle movements and sensory information.

  • Reproductive cell: Reproduction

  • Muscle cell: contraction and movement, contains contractile proteins - actin aand myosin.

• Plant Cells:

  • Root hair cell: Absorbs water and mineral ions from the soil through osmosis and active transport.

  • Palisade mesophyll cells: Primary site of photosynthesis in leaves; contains numerous chloroplasts.

Size of Specimens

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