Grade 10 Science First Semester Term Examination Reviewer

General Information

School: Batasan Hills National High School
Grade & Subject: Grade 10 Science
Term: First Semester Term Examination Reviewer
School Year: S.Y. 2026–2027
Basis: First Semester Term Examination TOS (Table of Specifications), summarizing the targeted TOS competencies.

Part I. Homeostasis

Definition of Homeostasis: Homeostasis is the maintenance of a relatively stable internal condition in the body even when the external environment changes.
Important Assessed Indicators:
- Body temperature
- Blood glucose level
- Blood pressure

1. Body Temperature Regulation

Response to Heat: When the body becomes too hot, sweating helps remove heat as sweat evaporates, allowing body temperature to move toward its normal range.
- Sequence: Hot body $\rightarrow$ sweating $\rightarrow$ evaporation $ ightarrow$ cooling $ ightarrow$ temperature returns toward normal.
Response to Cold: When the body becomes too cold, shivering helps produce heat and move body temperature toward normal.
Functional Summary:
- Sweating = cools the body.
- Shivering = produces heat.

2. Negative Feedback Mechanism

Definition: Negative feedback counteracts a change and helps return the body toward its normal condition.
Examples:
- Body becomes hot $\rightarrow$ sweating cools the body.
- Blood glucose rises $ ightarrow$ insulin helps lower blood glucose.
- Body becomes cold $ ightarrow$ shivering produces heat.

3. Positive Feedback Mechanism

Definition: Positive feedback strengthens or increases the original change until a particular event is completed.
Example:
- Childbirth $ ightarrow$ contractions $ ightarrow$ hormone release $ ightarrow$ stronger contractions $ ightarrow$ delivery.

Memory Guide for Feedback Mechanisms

Negative feedback: Reduces or reverses the change.
Positive feedback: Strengthens the change.

Part II. Natural Selection and Evolution

1. Natural Selection

Definition: Natural selection is a major mechanism of evolutionary change in which organisms with advantageous inherited traits are more likely to survive and reproduce.
Key Evolutionary Sequence:
- Variation $\rightarrow$ Selection $\rightarrow$ Differential survival $ ightarrow$ Reproduction $ ightarrow$ More common traits $ ightarrow$ Adaptation.
Illustrative Example:
- If a forest floor becomes darker, brown beetles may be less visible to predators.
- More brown beetles survive and reproduce, so brown coloration becomes more common over generations.
Important Misconception to Avoid: Organisms do not develop a trait simply because they need it. Individuals with inherited variations that provide an advantage are more likely to survive and reproduce.

2. Variation

Definition: Variation refers to differences in characteristics among individuals of the same population.
Examples of Inherited Characteristics:
- Height
- Hair type
- Beak size
- Body color
- Other inherited characteristics
Key Idea: Individuals in a population are not exactly identical.

3. Heredity

Definition: Heredity is the passing of characteristics from parents to offspring.
Memory Guide: Heredity = traits can be passed from parents to offspring.

Part III. Adaptation and Natural Selection

Adaptation

Definition: An adaptation is an inherited characteristic that helps an organism survive and reproduce in a particular environment.
Examples of Bird Beak Adaptations:
- Large, strong beak $\rightarrow$ crushing hard seeds
- Narrow beak $\rightarrow$ picking up small food
- Long beak $\rightarrow$ probing flowers/fruits
Environmental Scenario: If hard seeds become the major food available during a drought, birds with strong beaks may have an advantage.

Distinguishing Key Evolutionary Concepts

Variation: Differences already present in a population.
Natural Selection: Environmental conditions favor some variations.
Adaptation: An advantageous inherited characteristic that becomes useful in an environment.

Part IV. Evidence for Evolution

Comparative Morphology

Definition: Comparative morphology involves comparing the structures and body parts of organisms.

Homologous Structures

Definition: Homologous structures have a similar basic structural arrangement but may perform different functions.
Examples: Forelimbs of humans, whales, bats, cats, and birds.
Evolutionary Significance: Similar basic bone arrangements may suggest common ancestry even though functions differ.
Memory Guide: Similar structure + different function $\rightarrow$ Homologous structures.

Part V. Fossils as Evidence of Evolution

Role of Fossils: Fossils provide evidence of changes in organisms through geological time.
Fossil Observations Across Rock Layers:
- Oldest Rock Layer: Small body and several short toes
- Middle Rock Layer: Larger body and fewer toes
- Youngest Rock Layer: Larger body and one enlarged central toe
Important Conclusion: Populations showed structural changes over generations.

Part VI. Biogeography

Definition: Biogeography examines the distribution of organisms in different geographic areas.
Mechanisms: Geographic isolation can separate populations and reduce gene exchange. Over generations, separated populations may become increasingly different.
Memory Guide: Geographic isolation $\rightarrow$ reduced gene exchange $ ightarrow$ populations diverge $ ightarrow$ differences accumulate over generations.

Part VII. Combustion and Environmental Effects

Definition: Combustion is a chemical reaction that releases energy, usually involving a fuel and oxygen.
Interconnected Topics: Combustion connects with transportation, cooking, fuel use, smoke, air pollution, and environmental effects.
Key Idea: More unnecessary combustion can mean more emissions and greater potential environmental impact.
Possible Solutions:
- Walk when possible.
- Use cleaner energy sources when available.
- Avoid open burning.
- Dispose of waste properly.

Part VIII. Acids and Their Effects

Acids and Metals: Acids can react with some metals and cause corrosion (e.g., acid rain reacting with metal structures).
Acids and Carbonates: Acids can react with carbonate rocks such as limestone, causing them to wear away over time.

Part IX. Photosynthesis

Definition: Plants use sunlight, water, and carbon dioxide to produce food and release oxygen.
Simplified Chemical Concept Equation:

$\text{Carbon dioxide} + \text{Water} + \text{Light} \rightarrow \text{Food} + \text{Oxygen}$

Key Idea: Photosynthesis $\rightarrow$ produces oxygen.

Part X. Cellular Respiration

Definition & Function: Cellular respiration releases energy that cells can use for activities such as exercise, walking, running, studying, and other body activities.
Memory Guide: Cellular respiration $ ightarrow$ releases usable energy for cells.

Part XI. Acids, Bases, and Indicators

Classification and Indicator Results Table

Classification	Litmus Result	Red Cabbage Juice Result	Examples
Acid	Blue litmus $\rightarrow$ Red	Pink	Vinegar, calamansi/lemon juice
Base	Red litmus $\rightarrow$ Blue	Green	Soap solution, baking soda solution
Neutral	No change	Purple	Common salt solution, water

Part XII. Chemical Formulas

Definition: Chemical formulas show the elements and numbers of atoms present in a compound.
Target Chemical Compounds & Formulas:
- Sodium sulfate: $Na_2SO_4$
- Calcium chloride: $CaCl_2$
- Iron(III) chloride: $FeCl_3$
- Calcium carbonate: $CaCO_3$
Critical Rules & Consequences:
- An incorrect chemical formula can mislead users and cause errors when identifying or preparing chemicals.
- For ionic compounds, use the ion charges to determine the correct ratio of ions.

Part XIII. Law of Conservation of Mass

Statement of Law: Mass is neither created nor destroyed in a chemical reaction.
Atomic Mechanism: Atoms are rearranged, but the total number of atoms of each element remains the same.
Mathematical Equality:

$\text{Mass of reactants} = \text{Mass of products}$

Part XIV. Balancing Chemical Equations

Important Rule: Change coefficients, not subscripts, when balancing an equation.
Primary Goal: Have the same number of atoms of each element on both sides of the equation.

Balanced Chemical Equations

Hydrogen + Oxygen:

$2H_2 + O_2 \rightarrow 2H_2O$

Aluminum + Oxygen:

$4Al + 3O_2 \rightarrow 2Al_2O_3$

Methane Combustion:

$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$

Magnesium + Oxygen:

$2Mg + O_2 \rightarrow 2MgO$

Verification Procedure

To check an equation: count the atoms of every element on both sides. The numbers must be equal.

Quick Memory Guide

HOMEOSTASIS: Hot $\rightarrow$ Sweat $\rightarrow$ Cool; Cold $ ightarrow$ Shiver $ ightarrow$ Heat.
NEGATIVE FEEDBACK: Reduces/reverses the original change.
POSITIVE FEEDBACK: Strengthens the original change.
EVOLUTION: Variation $\rightarrow$ Heredity $ ightarrow$ Selection $ ightarrow$ Survival/Reproduction $ ightarrow$ Adaptation.
FOSSILS: Show changes through time.
BIOGEOGRAPHY: Geographic distribution and isolation support evolutionary divergence.
HOMOLOGOUS STRUCTURES: Similar basic structure, different functions $\rightarrow$ possible common ancestry.
ACID: Blue litmus turns red; cabbage juice becomes pink.
BASE: Red litmus turns blue; cabbage juice becomes green.
NEUTRAL: Litmus shows no change; cabbage juice remains purple.
CHEMICAL FORMULAS: $Na_2SO_4$ , $CaCl_2$ , $FeCl_3$ , $CaCO_3$ .
BALANCING: Count atoms $\rightarrow$ adjust coefficients $ ightarrow$ count again $ ightarrow$ equal atoms on both sides.

Final Study Checklist

[ ] Identify examples of homeostasis.
[ ] Explain negative and positive feedback.
[ ] Analyze situations involving temperature, glucose, and blood pressure.
[ ] Distinguish variation, heredity, isolation, selection, and adaptation.
[ ] Analyze evidence for natural selection.
[ ] Interpret fossil sequences.
[ ] Explain how homologous structures support evolution.
[ ] Explain how geographic isolation supports evolution.
[ ] Identify acids, bases, and neutral substances using indicators.
[ ] Interpret indicator-test results.
[ ] Write correct chemical formulas using ionic charges.
[ ] Apply the Law of Conservation of Mass.
[ ] Balance chemical equations by counting atoms.