BIOLOGY

Notes by graceconquers Senior High School Notes (STEM)

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●​ Proposed early ideas about biology and
LECTURE COVERAGE heredity. (coined biology)
●​ Suggested that organisms are made of cellular
1 Introduction Pg. 1 tissue and emphasized the importance of cells
in life processes.
2 Characteristic of Life Pg. 3
●​ Though more famous for his evolutionary ideas,
3 Cell Structure and Function Pg. 4 he contributed to early concepts about
organisms being composed of cells.
4 Tissue Pg. 4

5 Cellular Transport Pg. 8 Aristotle (384–322 BCE)

6 Cell Cycle Pg. 9

●​ Father of biology
7 Cancer Pg. 11 ●​ Ancient Greek philosopher and scientist.
Proposed that life comes from a vital force
(vitalism), and did not identify cells.
INTRODUCTION ●​ Though incorrect about spontaneous
generation, his ideas influenced biological
thinking for centuries.
●​ Biology is a natural science discipline that
studies living things.
●​ It is a very large and broad field due to the wide Antonie van Leeuwenhoek (1673–1680s)
variety of life found on Earth, so individual
biologists normally focus on specific fields.
●​ Improved microscopes and observed blood
●​ These fields are either categorized by the scale
cells, sperm cells, and microscopic organisms
of life or by the types of organisms studied.
he called “animalcules.”
●​ His discoveries revealed the existence of
1A KEY CONTRIBUTORS unicellular organisms, though he did not
observe cell division, and believed in
spontaneous generation.
Robert Hooke (1635–1703)

Robert Brown (1833)

●​ First to discover cells in 1665.
●​ Observed cork cells under a microscope
●​ coined the term "cell" from the Latin word cella, ●​ Identified the nucleus in plant cells, noting it as
meaning small room. a consistent and central component.
●​ Published his observations in Micrographia.
1B CELL
Jean-Baptiste de Lamarck (1744–1829)
●​ Cells are the basic, structural, and functional
units of all living organisms.
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Notes by graceconquers Senior High School Notes (STEM)
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●​ They are the smallest independent components ➢​ Size: 10–100 µm. Reproduce via mitosis
capable of carrying out all life processes. (asexual) and meiosis (sexual).
●​ Cells can exist as single-cell organisms ➢​ Contain many membrane-bound
(unicellular) or as part of multicellular organelles.
organisms.
●​ Cells are often called the "building blocks of life"
Function of Cell
because:
○​ They provide structure to the body. Function Description
○​ They convert nutrients into energy.
○​ They carry out specialized functions. Structure & Provides shape and support (e.g.,
○​ They contain hereditary material (DNA). Support skin cells, plant xylem).

Growth via Cells divide to allow growth and

Characteristics of Cell
Mitosis replace old/damaged cells.

●​ Provide structure and support. Transport of Active and passive transport of

●​ Enclosed by a cell membrane. Substances nutrients, gases, and waste.
●​ Contain cytoplasm where organelles are
suspended. Energy Mitochondria produce ATP;

●​ Have a nucleus (in eukaryotes) with genetic Production chloroplasts perform

material (DNA). photosynthesis.

●​ Contain organelles for energy production,

Reproduction Asexual (mitosis) and sexual
waste digestion, and synthesis of molecules.
(meiosis) reproduction.
●​ Perform life processes like reproduction,
metabolism, and transport.
1C CELL THEORY
Types of Cell

Principles
1.​ Prokaryotic Cells
➢​ Lack a true nucleus; have a nucleoid
1.​ All living organisms are composed of one or
region.
more cells (Matthias Schleiden’ 1838; Theodor
➢​ Single-celled organisms (e.g., bacteria,
Schwann, 1839)
archaea). Size: 0.1–0.5 µm.
2.​ The cell is the basic unit of structure and
➢​ Reproduce by binary fission.
function in living things Matthias Schleiden’
➢​ Simpler in structure.
1838)
2.​ Eukaryotic Cells
3.​ All cells arise from pre-existing cell Rudolf
➢​ Have a true, membrane-bound nucleus.
Virchow’ 1855)
➢​ Found in plants, animals, fungi, and
protists.

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Notes by graceconquers Senior High School Notes (STEM)
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managed by organs and
Significance systems.

Homeostasis The ability to maintain stable

●​ Marked a major conceptual shift in biology,
internal conditions (e.g.,
emphasizing the unity and continuity of life.
temperature, pH, water
●​ Unified botany and zoology under a common
balance).
principle.
●​ Provided the foundation for modern biological Energy Processing Organisms use energy to fuel
sciences, including genetics, molecular biology, their processes (photosynthesis,
and medicine. cellular respiration).

CHARACTERISTIC OF LIFE
2A ORGANIZATION OF LIFE

2A CHARACTERISTIC OF LIFE
Level Explanation

Characteristic Explanation Chemical Level Atoms like hydrogen and carbon

interact to form molecules.
Order Life is organized into cells,
tissues, organs, and systems. Molecular Level Molecules combine to form
Even unicellular organisms organelles (e.g., nucleus), which
show internal complexity. are parts of cells.

Sensitivity / Organisms detect and respond Cellular Level The cell is the smallest unit of life.
Response to stimuli (e.g., plants bend All life is made up of one or more
toward light, bacteria move cells.
toward nutrients).
Tissue Level Groups of similar cells and their
Reproduction All life can reproduce. surrounding materials performing
Single-celled organisms divide; a specific function. Four main
multicellular organisms tissue types: epithelial, connective,
produce offspring. muscle, nervous.

Growth and Life grows and develops Organ Level Two or more tissue types combine
Development following genetic instructions. to perform specific functions.
Offspring resemble parents. Examples: heart, lungs, stomach.

Regulation Internal functions like nutrient Organ System Groups of organs that work
transport and blood flow are Level together to perform major body
functions. Example: Urinary

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Notes by graceconquers Senior High School Notes (STEM)
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system (kidneys, bladder, ureters,
urethra).
3B CELL ORGANELLES
Organism Level A complete living being that may
be single-celled or multicellular
(like humans). All organ systems Organelle Function
work together in the organism.
Endoplasmic Synthesizes proteins (Rough ER),
Reticulum lipids (Smooth ER); transports
CELL STRUCTURE AND FUNCTION (ER) substances.

Golgi Bodies Packages and distributes proteins

3A CELL STRUCTURE AND COMPONENTS and lipids; forms lysosomes.

Ribosomes Site of protein synthesis.

Component Function
Mitochondria Powerhouse of the cell; generates
Cell Membrane Selectively permeable barrier; ATP (energy).
controls entry/exit of substances.
Lysosomes Contain enzymes to digest waste
Cell Wall Rigid outer layer in plant cells; and foreign materials.
provides structure and
protection. Chloroplast Site of photosynthesis; contains
(plants only) chlorophyll.
Cytoplasm Gel-like fluid inside cell; site for
chemical reactions. Vacuoles Store nutrients, waste products,
and water. Large in plant cells.
Nucleus Control center of the cell;
contains DNA.
TISSUE
Nucleolus Found in the nucleus; produces
ribosomes.
●​ Covers body surfaces and lines cavities;
○​ functions in protection
Nuclear Surrounds the nucleus; controls
○​ Secretion
Membrane material flow in/out of nucleus.
○​ absorption.
Chromosomes Carry genetic information; ●​ Classified based on cell shape and number of
humans have 23 pairs. layers.

4A EPITHELIAL TISSUE

●​ Function:
○​ Covers body surfaces
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○​ lines cavities 3.​ Stratified Columnar:
○​ protection, ➢​ Also rare; protection and secretion.
○​ secretion, ➢​ Example: Male urethra, some gland
○​ absorption, ducts.
○​ filtration
●​ Structure:
Pseudostratified Columnar Epithelium
○​ Cells are tightly packed with little
extracellular matrix.
○​ It may be simple (one layer) or stratified ●​ Appears layered but is a single layer with nuclei
(multiple layers), with cells shaped as at different levels.
squamous (flat), cuboidal (cube-like), or ●​ Often ciliated and contains goblet cells.
columnar (tall) ●​ Example: Lining of the respiratory tract.

Simple Epithelium (One layer of cells) Transitional Epithelium

1.​ Simple Squamous: ●​ Specialized for stretching; cells change shape

➢​ Thin and flat; allows diffusion and when tissue stretches.
filtration. ●​ Example: Urinary bladder
➢​ Example: Alveoli in the lungs.
2.​ Simple Cuboidal: 4B CONNECTIVE TISSUE
➢​ Cube-shaped; secretion and
absorption.
●​ Function:
➢​ Example: Kidney tubules.
○​ Supports, connects, and binds other
3.​ Simple Columnar:
tissues.
➢​ Tall cells; absorption and secretion.
○​ Also provides protection, insulation,
May have cilia or microvilli.
and transportation (e.g., blood).
➢​ Example: Lining of the stomach and
●​ Structure: Composed of specialized cells
intestines.
embedded in an extracellular matrix made of
fibers (collagen, elastic, reticular) and ground
Stratified Epithelium (Multiple layers) substance.

1.​ Stratified Squamous: Specialized Junctions

➢​ Protects against abrasion. Can be
keratinized or non-keratinized.
1.​ Desmosomes:
➢​ Example: Skin (keratinized), esophagus
➢​ Strong, spot-like adhesions that link the
(non-keratinized).
intermediate filaments of neighboring
2.​ Stratified Cuboidal:
cells, providing mechanical strength
➢​ Rare; protective.
and resistance to stress, especially in
➢​ Example: Sweat gland ducts.
tissues like skin and cardiac muscle.
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2.​ Adhering Junctions (Adherens Junctions): ➢​ Dense Regular: Fibers aligned in one
➢​ These junctions connect the actin direction; strong in tension.
cytoskeletons of adjacent cells via ○​ Example: Tendons and
cadherin proteins, creating a ligaments.
continuous belt-like structure around ➢​ Dense Irregular: Fibers in multiple
cells/cementing directions; resists tension in many
➢​ They help maintain tissue shape and directions.
integrity by holding cells tightly ○​ Example: Dermis of skin.
together and coordinating cell ➢​ Elastic: Contains elastic fibers; allows
movement. recoil.
3.​ Tight Junctions: ○​ Example: Walls of large arteries.
➢​ Form a seal between adjacent cells,
preventing the passage of molecules
Supporting Connective Tissue
between them.
➢​ This junction regulates selective
permeability and maintains barrier 1.​ Cartilage: Semi-solid, flexible tissue; lacks
functions in epithelial and connective blood vessels.
tissue interfaces. ➢​ Hyaline Cartilage: Smooth; reduces
4.​ Gap Junctions: friction. Example: Trachea, ends of long
➢​ Specialized channels that allow the bones.
direct transfer of ions, nutrients, and ➢​ Elastic Cartilage: Flexible and resilient.
signaling molecules between Example: External ear.
neighboring cells, enabling rapid ➢​ Fibrocartilage: Tough and
communication and coordination of compressible. Example: Intervertebral
cellular activities, such as in cardiac discs, pubic symphysis.
and smooth muscle tissues. 2.​ Bone (Osseous Tissue): Hard matrix with
calcium salts and collagen fibers.
➢​ Function: Supports, protects, and stores
Connective Tissue Proper
minerals.
➢​ Contains osteons (Haversian systems)
1.​ Loose Connective Tissue (More ground for structure and nutrient flow.
substance, fewer fibers):
➢​ Areolar: Binds skin to muscles,
Fluid Connective Tissue
surrounds organs and blood vessels.
➢​ Adipose: Stores fat, cushions organs,
insulates. 1.​ Blood:
➢​ Reticular: Supports lymphoid organs a.​ Matrix: Liquid plasma.
(lymph nodes, spleen, bone marrow). b.​ Components:
2.​ Dense Connective Tissue (More fibers, less ➢​ Red Blood Cells (Erythrocytes):
ground substance): Transport oxygen.

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➢​ White Blood Cells (Leukocytes):
Immune defense.
Cardiac Muscle
➢​ Platelets (Thrombocytes): Blood
clotting.
●​ Appearance: Striated like skeletal muscle but
with branched fibers and usually one nucleus
4C MUSCLE TISSUE
per cell; contains intercalated discs for
synchronized contractions.
●​ Muscle tissue is specialized for contraction, ●​ Control: Involuntary—controlled by the
enabling movement of the body and internal autonomic nervous system.
structures. ●​ Function: Pumps blood throughout the body.
●​ Muscle cells, also called muscle fibers, contain ●​ Location: Found only in the heart.
protein filaments (actin and myosin) that slide
past each other to produce force and
4D NERVOUS TISSUE
movement.

●​ Nervous tissue is the body’s main

Skeletal Muscle
communication network, specialized for
receiving stimuli and transmitting electrical
●​ Appearance: Long, cylindrical fibers with impulses to coordinate body functions.
multiple nuclei; striated (striped appearance).
●​ Control: Voluntary—under conscious control.
Key Components
●​ Function: Responsible for body movements,
posture, and heat production.
●​ Location: Attached to bones via tendons (e.g., 1.​ Neurons
biceps, triceps). ➢​ The functional units of the nervous
system.
➢​ Composed of a cell body (soma),
Smooth Muscle
dendrites (receive signals), and an axon
(sends signals).
●​ Appearance: Spindle-shaped cells with a single ➢​ Responsible for sensing stimuli,
nucleus; non-striated. processing information, and
●​ Control: Involuntary—not under conscious transmitting signals to other neurons,
control. muscles, or glands.
●​ Function: Controls slow, sustained contractions 2.​ Neuroglia (Glial Cells)
to move substances through internal organs. ➢​ Supportive cells that nourish, protect,
●​ Location: Walls of hollow organs such as the and insulate neurons.
digestive tract, blood vessels, urinary bladder, ➢​ Do not transmit electrical impulses but
and uterus. are essential for maintaining a healthy
neural environment.

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Notes by graceconquers Senior High School Notes (STEM)
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●​ Concept: Driven by kinetic energy and results
Location
in dynamic equilibrium where concentrations
are equal on both sides of the membrane.
●​ Found in the brain, spinal cord, and peripheral
nerves.
Osmosis
●​ Functions in sensation, thought processing,
motor control, and regulation of internal organ
activity. ●​ The diffusion of water through a selectively
permeable membrane from an area of high
CELLULAR TRANSPORT water concentration to low water
concentration.
●​ Membrane: Semi-permeable (allows small
●​ If a cell were a house, the plasma membrane
molecules like water but not large ones like
would be its walls, with windows and doors to
glucose).
control what goes in and out.
●​ Osmosis Scenarios:
●​ The plasma membrane is crucial for
○​ Hypertonic: Solution has more solute →
maintaining cellular balance by regulating the
water moves out → cell shrinks
entry and exit of substances.
(crenation).
●​ This occurs through two primary types of
○​ Isotonic: Equal solute concentration →
transport:
no net water movement → cell stays the
○​ Passive Transport – does not require
same.
energy.
○​ Hypotonic: Solution has less solute →
○​ Active Transport – requires cellular
water moves in → cell swells and may
energy (ATP).
burst (lysis).
●​ Red Blood Cells:
5A PASSIVE TRANSPORT ○​ Hypertonic: Shrinks.
○​ Isotonic: Normal.
●​ Passive transport moves substances from a ○​ Hypotonic: Swells/lyses.
region of high concentration to low
concentration—down the concentration Facilitated Diffusion
gradient—without using energy.
●​ The three main types of passive transport are:
●​ Movement of large or charged molecules via
transport proteins.
Simple Diffusion ●​ Types:
○​ Channel Proteins: Open pores for small
●​ Movement of small or nonpolar molecules (e.g., ions or water to flow through.
O₂, CO₂) across the membrane without the aid ○​ Carrier Proteins: Bind to a specific
of proteins. molecule, change shape, and carry it
●​ Example: Smelling food from another room; across.
oxygen diffusing into cells.
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○​ Examples: Glucose and ions like Na⁺ or ●​ Much like the life cycle of a butterfly or human,
Cl⁻. the cell undergoes various developmental steps
to grow, replicate its DNA, and divide.
●​ The cell cycle is divided into two main phases:
5B ACTIVE TRANSPORT
○​ Interphase – the cell prepares for
division.
●​ Active Transport and Homeostasis (Requires
○​ Mitotic (M) phase – the cell divides into
Energy – ATP)
two.
●​ Active transport moves substances against the
concentration gradient, from low to high
concentration, using energy. 6A INTERPHASE
●​ It maintains cellular conditions necessary for
homeostasis. ●​ Interphase is the longest phase of the cell cycle
where the cell is not dividing but is actively
preparing for cell division.
Pump Transport
●​ Cell performs normal functions, grows,
replicates DNA, and produces RNA
●​ Primary Active Transport: Direct use of ATP
(e.g., Sodium-Potassium Pump).
Phases
●​ Secondary Active Transport: Uses energy from
gradients created by primary transport.
1.​ G₁ phase (First Gap): The cell grows, produces
organelles, and builds necessary molecules.
Vesicle Transport
2.​ S phase (Synthesis): The cell copies its DNA and
duplicates its centrosomes.
●​ Exocytosis: Vesicles expel materials (e.g., 3.​ G₂ phase (Second Gap): The cell grows more,
hormones, waste) out of the cell. synthesizes proteins and organelles, and
●​ Endocytosis: Cell takes in materials via vesicles. prepares for mitosis.
○​ Pinocytosis: "Cell drinking" – fluids. 4.​ G0 phase - Some cells exit the cycle from G₁
○​ Phagocytosis: "Cell eating" – large and enter a resting state; Cells in G₀ do not
particles or microorganisms. divide (e.g., neurons); Can be temporary or
Receptor-Mediated permanent
○​ Endocytosis: Specific molecules bind to
receptors before being brought in.
Checkpoint
-​ Between G₁ and S phase
CELL CYCLE -​ Between G₂ and G0

●​ The cell cycle is the life cycle of a cell,

●​ After interphase, the chromatin further
encompassing the stages from its formation to
condensed up to 10,000 times into itself to form
its division into two daughter cells.
set of chromosomes

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6B MITOSIS In animal cells, once the chromosomes are divided,

the cells develop contractile rings that are composed
●​ Body cells of actin microfilaments and bundles of the protein
●​ Division of nucleus into genetically identical tubulin that form microtubules. During cytokinesis,
daughter nuclei the contractile ring forms around the inside of the
cell membrane

Phases
Plant cells cannot form contractile rings because
they contain cell walls
1.​ Prophase: Chromosomes condense, spindle
fibers begin to form, and the nucleolus
disappears.

Centrioles are only present in animal cell and

lower in plant cell

2.​ Prometaphase: The nuclear envelope breaks

down, and microtubules attach to chromosomes
at kinetochores.
3.​ Metaphase: Chromosomes align at the
metaphase plate; the spindle checkpoint
ensures proper attachment.
4.​ Anaphase: Sister chromatids separate and 6C MEIOSIS
move to opposite poles of the cell.

●​ A form of cell division that produces gametes

There are times that during anaphase, (egg and sperm) with half the number of
chromosomes fail to separate properly. This chromosomes (haploid) compared to the parent
results to nondisjunction, wherein cell have cell.
abnormal no. of chromosomes ●​ Occurs only in sexually reproducing organisms
Involved in gametogenesis:
○​ Spermatogenesis – formation of sperm
5.​ Telophase: Nuclear membranes reform around
○​ Oogenesis – formation of eggs
each set of chromosomes, and chromosomes
●​ Consists of two successive divisions:
begin to decondense.
○​ Meiosis I – reduces chromosome
6.​ Cytokinesis: In animal cells, a contractile ring
number
of actin filaments forms a cleavage furrow,
○​ Meiosis II – separates sister chromatids
pinching the cell in two. In plant cells, vesicles
●​ Results in four genetically unique haploid cells
form a cell plate in the center, which develops
●​ Fusion of sperm and egg forms a zygote
into a new cell wall dividing the cell.
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Notes by graceconquers Senior High School Notes (STEM)
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○​ Zygote is diploid (restores full 3.​ Anaphase II: Sister chromatids separate to
chromosome number) opposite poles
●​ Triggered by hormones: ​ 4.​ Telophase II: Nuclear envelope reforms Spindle
○​ Estrogen (mainly female) fibers disassemble
○​ Testosterone (mainly male) 5.​ Cytokinesis II: Cytoplasm divides → 4
●​ Sex chromosomes: non-identical haploid daughter cells
○​ X from mother
○​ Y from father
○​ XX = Female
○​ XY = Male

Meiosis I (Reductional Division)

Reduces chromosome number by half

1.​ Prophase I: Nuclear envelope breaks down

Chromosomes condense Spindle fibers form
2.​ Prometaphase I: Spindle fibers attach to
centromeres
3.​ Metaphase I: Homologous chromosomes align
at the equatorial plate Crossing over may occur
(genetic variation)
4.​ Anaphase I: Homologous chromosomes
separate to opposite poles
5.​ Telophase I: Spindle fibers disappear Nuclear
envelope reforms
6.​ Cytokinesis I: Cytoplasm divides → 2 haploid
cells form (non-identical)
CANCER

Meiosis II (Equational Division)

●​ Cancer is a disease where cells grow
uncontrollably and invade surrounding tissues.
1.​ Prophase II: Chromatin condenses into ●​ It begins when mutations occur in genes that
chromosomes Nuclear envelope breaks down regulate cell division.
Centrosomes move to opposite poles Spindle ●​ Causes of Cancer:
fibers reform ○​ Missense mutations (changes in DNA
2.​ Metaphase II: Chromosomes align at the sequence)
center (not homologous pairs) ○​ Oncogenes: Mutated genes that
promote cancer
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○​ Cancer develops when mitosis is not ●​ Unhealthy lifestyle (e.g., poor diet, lack of
properly controlled and cells ignore exercise)
checkpoints in the cell cycle ●​ Age
●​ Chronic inflammation
●​ Immune system suppression
7A TUMOR
●​ Sun exposure

●​ A tumor starts from a single mutated cancer

cell that divides uncontrollably.
●​ The cancer cells invade nearby tissues, 7B BODY’S DEFENSE
disrupting normal function.
●​ Cancer cells enter the lymphatic system or
Immune Cell Type Function
blood vessels and spread to other parts of the
body, forming secondary tumors. T cells (T Recognize and destroy
lymphocytes) cancerous cells
Types of Tumor
NK cells (Natural Recognize and kill
Tumor Description Killer cells) virus-infected or cancerous
Type cells

Benign Non-cancerous, does not spread, and Macrophages Engulf and digest abnormal
is treatable cells

Malignant Cancerous, invasive, can spread to Dendritic cells Initiate immune response
nearby or distant tissues (metastasis) by presenting antigens

B cells (B Produce antibodies to target

Progression of Cancer lymphocytes) cancer cells

1.​ Tumor forms from a single cancerous cell Cell Cycle Control & Cancer:
2.​ Cancer cells invade neighboring tissues -​ Cyclins and Cyclin-dependent kinases (CDKs)
3.​ Cancer cells spread via lymphatic system or regulate the cell cycle progression
blood vessels -​ Mutations in cyclins or CDKs can lead to loss
of control, contributing to cancer
7B RISK FACTORS development

●​ Genetics / Family history

●​ Exposure to carcinogens (e.g., tobacco,
radiation, chemicals)
●​ Hormonal factors

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