Biology Test Grade [10]

7 Characteristics Of Life

Cellular Organization:
- All living things are composed of one or more cells, which are considered the basic units of life.
Homeostasis:
- The ability to maintain a stable internal environment despite external changes. This includes regulating temperature, pH, and other vital conditions.
Metabolism:
- The sum of all chemical reactions that occur within an organism. This involves converting energy from the environment into forms that can be used by cells, such as ATP.
Growth and Development:
- Living organisms undergo regulated growth and developmental processes. This includes cell division and differentiation in multicellular organisms.
Reproduction:
- The ability to produce new organisms. Reproduction can be asexual (involving one parent, producing genetically identical offspring) or sexual (involving two parents, producing genetically diverse offspring).
Response to Stimuli:
- The ability to respond to environmental changes or stimuli. This can include movement, changes in behavior, or physiological adjustments.
Evolution and Adaptation:
- Over generations, living organisms undergo adaptation and evolution, leading to changes that enhance survival and reproduction in changing environments.

Cell Theory

All living organisms are composed of one or more cells:
- This principle establishes that cells are the basic units of structure and function in all living things. Whether an organism is unicellular (like bacteria) or multicellular (like plants and animals), cells are the building blocks of life.
The cell is the basic unit of life:
- Cells are the smallest units that can carry out all the processes necessary for life. This includes metabolism, growth, reproduction, and response to the environment.
All cells arise from pre-existing cells:
- This tenet emphasizes that new cells are created by the division of existing cells. It refutes the idea of spontaneous generation and underscores the continuity of life through cellular reproduction.

Plant and Animal Structures

Nucleus:
- Structure: Double membrane-bound organelle with nuclear pores; contains chromatin and nucleolus.
- Function: Stores DNA; coordinates cell activities like growth, metabolism, and reproduction; site of transcription.
Nucleolus:
- Structure: Dense, spherical structure within the nucleus.
- Function: Synthesizes ribosomal RNA (rRNA) and assembles ribosome subunits.
Ribosomes:
- Structure: Composed of rRNA and protein; found free-floating in the cytoplasm or attached to the ER.
- Function: Protein synthesis.
Endoplasmic Reticulum (ER):
- Structure: Network of membranous tubules and sacs; two types: rough ER (with ribosomes) and smooth ER (without ribosomes).
- Function: Rough ER synthesizes proteins; smooth ER synthesizes lipids, detoxifies chemicals, and stores calcium ions.
Golgi Apparatus:
- Structure: Stacks of flattened membranous sacs.
- Function: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Mitochondria:
- Structure: Double membrane-bound with inner folds called cristae.
- Function: Produces ATP via cellular respiration; powerhouse of the cell.
Chloroplasts:
- Structure: Double membrane-bound with internal stacks of thylakoids called grana, containing chlorophyll.
- Function: Conducts photosynthesis to convert solar energy into chemical energy stored in glucose.
Lysosomes:
- Structure: Membrane-bound vesicles containing hydrolytic enzymes.
- Function: Digests macromolecules, old cell parts, and microorganisms; involved in apoptosis.
Peroxisomes:
- Structure: Small, membrane-bound organelles with enzymes.
- Function: Breaks down fatty acids and detoxifies harmful substances.
Cytoskeleton:
- Structure: Network of protein fibers (microtubules, microfilaments, intermediate filaments).
- Function: Provides structural support, enables cell movement, and aids intracellular transport.
Plasma Membrane:
- Structure: Phospholipid bilayer with embedded proteins.
- Function: Regulates passage of materials in and out of the cell; provides protection and support.
Large Central Vacuole:
- Structure: Large membrane-bound sac.
- Function: Stores water, nutrients, and waste products; helps maintain turgor pressure for structural support.
Cell Wall:
- Structure: Rigid outer layer composed of cellulose.
- Function: Provides structural support and protection; maintains cell shape.
Plasmodesmata:
- Structure: Channels through the cell walls that connect adjacent plant cells.
- Function: Allows transport and communication between plant cells.
Amyloplasts:
- Structure: Non-pigmented organelles.
- Function: Synthesize and store starch granules.
Chromoplasts:
- Structure: Organelles containing pigments other than chlorophyll.
- Function: Responsible for pigment synthesis and storage, contributing to the color of fruits and flowers.

Cell Cycles

1. Interphase

Interphase is the period of growth and preparation for cell division. It consists of three stages:

G1 Phase (Gap 1):
- Function: The cell grows in size, produces RNA, and synthesizes proteins necessary for DNA replication. It is a period of intense biochemical activity.
- Checkpoint: At the end of G1, the cell checks for DNA damage and ensures that all necessary growth factors and nutrients are present.
S Phase (Synthesis):
- Function: DNA replication occurs, resulting in the duplication of the chromosomes. Each chromosome now consists of two sister chromatids.
- Checkpoint: Ensures that DNA replication has been accurately completed.
G2 Phase (Gap 2):
- Function: The cell continues to grow and produces proteins and organelles. It also begins reorganizing its contents in preparation for mitosis.
- Checkpoint: The cell checks for DNA damage post-replication and ensures all DNA is replicated correctly.

2. Mitotic Phase (M Phase)

This phase involves the division of the cell's nucleus and cytoplasm, resulting in two daughter cells. It consists of mitosis and cytokinesis:

Mitosis: Divided into several stages:
- Prophase: Chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down. The mitotic spindle starts to form.
- Metaphase: Chromosomes line up along the metaphase plate (equatorial plane) of the cell. The spindle fibers attach to the centromeres of the chromosomes.
- Anaphase: Sister chromatids are pulled apart by the spindle fibers and move toward opposite poles of the cell.
- Telophase: Chromatids reach the poles, de-condense back into chromatin, and are enclosed by a re-forming nuclear envelope.
Cytokinesis: The cytoplasm of the cell divides, creating two separate daughter cells. This process differs slightly between plant and animal cells:
- In Animal Cells: A cleavage furrow forms to split the cell.
- In Plant Cells: A cell plate forms along the center line of the cell, eventually developing into a separating cell wall.

Cell Cycle Control

The cell cycle is tightly regulated by checkpoints, signaling pathways, and proteins such as cyclins and cyclin-dependent kinases (CDKs) to ensure proper division and prevent errors, such as DNA damage or incomplete replication.

Disruptions in the cell cycle control mechanisms can lead to uncontrolled cell division, a hallmark of cancerous growths. Understanding the cell cycle is crucial for developing treatments for various diseases, including cancer.

Diffusion and Osmosis

Diffusion and osmosis always cause particles to move from a region of higher concentration to a region of lower concentration. This movement continues until equilibrium is reached, where the concentration of particles is uniform throughout the space or across the membrane.

Diffusion refers to the movement of particles (such as gases or solutes) from an area of higher concentration to an area of lower concentration.
Osmosis is a specific type of diffusion that involves the movement of water molecules across a semipermeable membrane from an area of higher water concentration (or lower solute concentration) to an area of lower water concentration (or higher solute concentration).

Levels of Organization

Atom/Molecule: Atoms are the basic units of matter that form molecules, which are groups of atoms bonded together.
Cell: The basic unit of life, where molecules come together to perform life functions.
Tissue: Groups of similar cells working together to perform a specific function.
Organ: Structures composed of different tissues working together to perform specific functions.
Organ System: Groups of organs that work together to perform complex functions necessary for the organism's survival.
Organism: An individual living entity that can function independently.
Population: A group of organisms of the same species living and interacting in a particular area.

Type of Tissues

Epithelial Tissue:
- Function: Covers the body surfaces, lines hollow organs and cavities, and forms glands.
- Characteristics: Cells are closely packed with minimal extracellular material. This tissue acts as a barrier to protect the body, absorbs nutrients, and secretes substances.
- Examples: Skin epithelium, lining of the gastrointestinal tract, and glandular tissue.
Connective Tissue:
- Function: Supports, binds together, and protects tissues and organs of the body.
- Characteristics: Contains a large amount of extracellular matrix with various types of cells embedded within it.
- Examples: Bone, blood, adipose (fat) tissue, cartilage, and tendons.
Muscle Tissue:
- Function: Responsible for movement, whether voluntary or involuntary.
- Characteristics: Composed of cells that have the ability to contract and generate force.
- Types:
  - Skeletal Muscle: Voluntary muscles attached to bones, enabling movement.
  - Cardiac Muscle: Involuntary muscle found in the walls of the heart, responsible for pumping blood.
  - Smooth Muscle: Involuntary muscle found in the walls of internal organs, such as the intestines and blood vessels, controlling movements like peristalsis.
Nervous Tissue:
- Function: Transmits electrical impulses throughout the body, enabling communication between different body parts.
- Characteristics: Composed of neurons, which transmit impulses, and glial cells, which provide support and protection for neurons.
- Examples: Brain, spinal cord, and peripheral nerves.