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Stem Cells and Specialized Plant and Animal Cells and Tissues

REGENERATION

Definition: The process wherein a body part is replaced or re-grown, primarily through mitosis.
Examples:
  - Salamanders: Capable of regrowing amputated limbs.
  - Liver: The only human organ with natural regeneration capabilities.
  - Fingertips: Exhibit limited regenerative abilities.

Cell Specialization

Concept: All cells share the same DNA, yet they perform unique functions and may differ in appearance.
Key Term: Cell Differentiation - Process by which a cell becomes specialized to fulfill specific functions.

Cellular Differentiation

Definition: The process of creating specialized cells from unspecialized cells.
Origin: All body cells descend from a zygote that undergoes mitosis.
Embryonic Development: As the embryo matures, cells undergo changes in shape, content, and function.

Embryonic Development Stages

Zygote: The initial cell formed when a sperm and egg unite.
Blastocyst: The stage following the zygote where cell differentiation begins.
Gastrula: The stage where three primary germ layers form:
  - Ectoderm: External layer.
  - Mesoderm: Middle layer.
  - Endoderm: Internal layer.

Types of Differentiated Cells

Germ Cells: E.g., sperm and egg.
Specialized Cells:
  - Skin cells (epidermis)
  - Neurons (brain cells)
  - Pigment cells
  - Cardiac muscle cells
  - Skeletal muscle cells
  - Tubule cells (kidney)
  - Red blood cells
  - Smooth muscle cells
  - Pancreatic cells
  - Thyroid cells
  - Lung cells

What is a Specialized Cell?

Definition: A cell designed to perform a specific function.
Differences: Specialized cells exhibit distinct physical and chemical characteristics enabling them to execute their roles effectively.
Examples:
  - Neurons
  - Blood cells
  - Fat cells
  - Muscle cells
  - Bone cells

Why Specialize?

Unicellular Organisms: Operate all necessary functions within a single cell, e.g., Amoeba.
Multicellular Organisms: Greater complexity necessitates specialization to supply nutrients, transport materials, eliminate waste, and combat infections.

What Causes Specialization?

Cytoplasm Differences:
- Asymmetric distribution of organelles and factors in the zygote leads to different daughter cells.
Environmental Conditions:
- Variations in temperature and nutrient availability influence cell differentiation.
Neighboring Cells:
- Substances produced by adjacent cells can diffuse, impacting neighboring cells' functionality.

Outcome: Expression of different genes may occur due to these factors.
- Example: Mitosis results in two daughter cells with identical DNA but potentially different gene expressions (e.g., neuron-specific vs. epithelial-specific genes).

Origin of Specialized Cells

Source: Every cell in the body arises from unspecialized Stem Cells.
Stem Cells: Possess the capability to transform into any cell type under appropriate conditions.
Potential Use: The capacity to direct stem cell development holds promise for treating injuries and diseases.

Types of Stem Cells

Embryonic Stem Cells

Source: Derived from human embryos (including umbilical cords, placenta, or aborted embryos).
Characteristic: Pluripotent; these cells can differentiate into any cell type.

Adult Stem Cells (Somatic Cells)

Occurrence: Scattered throughout the body but in few areas since most cells are specialized.
Locations: Found mainly in the brain, bone marrow, blood vessels, skeletal muscle, skin, teeth, heart, and liver.
Function: They multiply to replenish dying cells and repair damaged tissues, presenting multipotent differentiation abilities.

Meristematic Stem Cells

Definition: Stem cells found in plants.
Location: Located in the growing tips of roots and branches.
Function: Continuously produce new cell types throughout the plant's life.

Animal Tissues

Definition: Groups of specialized cells working together for shared tasks. There are four main types:
  1. Epithelial tissue
  2. Connective tissue
  3. Muscle tissue
  4. Nervous tissue

1) Epithelial Tissue

Function: Lines body cavities and the outer body surface, providing a protective barrier.
Characteristics:
- Varies in thickness (one or multiple layers).
- Forms glands for hormone and enzyme secretion.
Example: Skin.

2) Connective Tissue

Purpose: Joins other tissues and provides support, strength, and fat storage.
Types:
  1. Supporting:
     - a) Bone
     - b) Cartilage
  2. Binding:
     - a) Tendons
     - b) Ligaments
  3. Fibrous:
     - a) Adipose (fat)
     - b) Blood
Blood Composition: Made of plasma, red blood cells, white blood cells, and platelets.

3) Muscle Tissue

Types:
  - Cardiac
  - Skeletal
  - Smooth
Function:
  - Skeletal muscles enable movement of appendages.
  - Smooth muscle lines several organs.
  - Cardiac muscle constitutes heart muscle.
  - Smooth and cardiac muscles are involuntary, functioning without conscious control.

4) Nervous Tissue

Functionality: Capable of receiving and transmitting messages within the body, thus coordinating actions.
Specific Roles:
- Relay signals from the brain or spinal cord to muscles and glands.
- Detect environmental stimuli and activate body responses (e.g., reacting to heat).

Animal Tissues Summary

Tissue Type	Description	Function	Example
Connective Tissue	Various types of cells and fibers held together by a matrix	Support, Insulation	Bone, Blood, Fat, Tendons
Epithelial Tissue	Thin sheets of tightly packed cells covering surfaces	Protection from dehydration, low-friction surfaces	Skin, Lining of respiratory/digestive system
Muscle Tissue	Bundles of long muscle fibers capable of contraction	Movement	Skeletal muscle, Smooth muscle, Cardiac muscle
Nervous Tissue	Long, thin cells that conduct electrical impulses	Sensory, Communication, Coordination of body functions	Brain, Nerves in sensory organs

Tissues in the Arm

Epithelial Tissue: Lines body surfaces.
Connective Tissues: Includes specialized structures like loose connective tissue, providing padding.
Muscle Tissue: Composed of fibers that contract for movement.
Nervous Tissue: Consists of signal-transmitting cells.
Connective Tissue Types:
- Bone and cartilage: Made of cells in a hard matrix.
- Blood: A fluid connective tissue.

Plant Tissues

Types:
  - Epidermal
  - Vascular
  - Ground
  - Meristematic
Origin: All plant tissues arise from unspecialized meristematic tissue.

1) Meristematic Tissue

Characteristics: Unspecialized tissue that differentiates into various cell types.
Location: Found at root tips, responsible for plant growth.

2) Epidermal Tissue

Function: Protective outer layer of plants.
Feature: Contains specialized guard cells that form stomata for gas and water exchange.

3) Ground Tissue

Functions:
  - Provides structural support in stems.
  - Performs photosynthesis and gas exchange in leaves, primarily in the mesophyll layer.
  - Stores water and nutrients in roots.

4) Vascular Tissue

Role: Responsible for transporting substances throughout the plant.
Types:
- Xylem: Transports water and minerals from roots to leaves.
- Phloem: Distributes sugars produced during photosynthesis to other plant parts.

Plant Tissues Summary

Tissue Type	Description	Major Functions
Epidermal tissue	Clear, thin outer covering of the plant	Forms a protective barrier; allows exchange of water, CO2, and O2
Vascular tissue	Conducts materials	Xylem: Moves water and minerals; Phloem: Transports sugars
Ground tissue	Comprises most of the plant	Stem: provides support; Root: stores nutrients; Leaf: site of photosynthesis
Meristematic Tissue	Responsible for plant growth	Unspecialized tissue capable of division by mitosis.

Seatwork / Homework

Reading Assignment: Read Section 1.3 p.38-45.
Learning Checks:
- p.41 #1-5
- p.45 #1-5
Check and Reflect: p.47 #1-6, 8, 10, 12, 14, 17.