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Grade 6 Science Notes and Review Questions (DepEd-Based): Second Quarter

Quick notes in outline form and practice questions to help learners review the topics covered in Grade 6 Science (Second Quarter) based on the DepEd curriculum.

This page contains quick notes and review questions for the following topics in Grade 6 Science – Second Quarter: 

  • Module 1: Human Body Systems: Skeletal, Integumentary, and Digestive Systems
  • Module 2: Human Body Systems: Respiratory, Circulatory, and Nervous Systems
  • Module 3/4: Animals: Characteristics of Vertebrates
  • Module 5: Animals: Characteristics of Invertebrates
  • Module 6: Ecosystem: Tropical Rainforests, Coral Reefs, and Mangrove Swamps

You can download printable (PDF) copies of the notes and the practice exam below.

Science 6: Quick Notes

Quarter 2 Module 1: Human Body Systems: Skeletal, Integumentary, and Digestive Systems

Skeletal System


  • framework of the body
  • consists of 206 bones (adult) that are connected by ligaments

Major functions of skeletal system:

  • body support
  • facilitation of movement
  • protection of internal organs
  • storage of minerals and fats
  • blood cell formation

Two divisions of the skeletal system:

  • axial skeleton – includes skull, vertebral column, ribs, and sternum
  • appendicular skeleton – includes the bones of the shoulder, arms, hands, hips, legs, and feet

Classification of bones:

  • long bones – limbs like arms and legs
  • short bones – wrist and ankles
  • flat bones – shoulder blades and skull
  • irregular bones – face and vertebrae

Selected bones:

  • skull – consists of:
    • cranium – protects the brain
    • facial bones
  • spinal column / vertebrae
    • protects the spinal cord
    • 33 in child, 26 in adult
  • rib cage
    • protects the lungs and heart
    • 12 pairs
      • upper 7 pairs – true ribs, connected to the breastbone
      • 8th to 10th pairs – connected to the 7th rib by cartilage
      • last 2 pairs – floating ribs, not connected to sternum or other rib
  • scapula – bone at the back of shoulder
  • humerus – long bone in the upper arm
  • radius – the thicker of the two bones in the forearm
  • ulna – the longer of the two bones in the forearm
  • wrist or carpals – 8 bones that connect the hand to the forearm
  • palm or metacarpals – 5 bones

Bone marrow

  • found inside bones
  • manufacture red blood cells
  • two types:
    • red bone marrow – found in the humerus, femur, pelvis and vertebrae
    • yellow bone marrow – found in many other bones

Integumentary System

Integumentary system consists of:

  • skin
  • hair – helps keep you warm
  • nails – give structure to the ends of the fingers
  • glands – release oils for moisture and protection
  • nerves – send and receive messages to/from the brain

Functions of the integumentary system:

  • barrier to protect the body from the outside environment
  • one of the first lines of defense of the body against pathogens
  • helps retain body fluids, protect against dehydration
  • helps eliminate waste products
  • helps regulate body temperature
  • acts as a receptor for touch, pressure, pain, heat, and cold
  • stores water and fat

Parts of the skin:

  • epidermis
    • outer layer of the skin
    • outer epidermal cells secrete a protein called keratin
  • dermis
    • layer directly below the epidermis
    • connective tissues prevent the skin from tearing and enable it to return to normal after stretching
  • hypodermis
    • layer below the dermis
    • stores fats and helps the body retain heat
  • sweat glands
    • small tubular structures that produce sweat
    • also known as sudoriferous or sudoriparous glands
  • hair
    • hair root – part of the hair below the surface of the skin
    • hair shaft – visible part of the hair that protrudes through the skin
  • melanocytes
    • produce melanin, the pigment responsible for skin color
    • located in the epidermis

Digestive System

Digestive system is composed of:

  • mouth
  • esophagus
  • stomach
  • small intestine
  • large intestine


  • where digestion begins
  • teeth – cut and grind food
  • saliva – moistens the food
  • ptyalin – enzyme in saliva that helps digest starch


  • peristalsis – rhythmic, wave-like muscle movements that push the food down


  • food broken down into smaller pieces
  • gastric juices split proteins and fats

Small intestine

  • 7 meters long
  • where final digestion takes place and food is absorbed

Large intestine

  • where undigested food goes
  • also temporarily stores water
  • feces – waste products of digestion
  • rectum – lower part of the large intestine that stores feces until elimination through the anus

Quarter 2 Module 2: Human Body Systems: Respiratory, Circulatory, and Nervous Systems

Respiratory System


  • the exchange of gases with the environment
  • includes:
    • intake of oxygen
    • delivery of oxygen to the different parts of the body
    • release of carbon dioxide

Nasal cavity

  • nostrils – opening into the nasal passages
  • lined with hair and glands that produce mucus that traps impurities in the air


  • the throat
  • common passageway for food, water, and air


  • contains vocal cords that vibrate when air passes by


  • the windpipe
  • also filters the air we inhale


  • the two tubes that carry air into the lungs


  • smaller tubes after the bronchi
  • branch off into alveoli


  • grape-like structures at the end of each bronchiole
  • surrounded by capillaries
  • the exchange of oxygen and carbon dioxide happens between the alveoli and capillaries


  • main organ of the respiratory system
  • where gas exchange occurs


  • dome-shaped muscle that controls breathing
  • located at the bottom of the lungs

Circulatory System

Circulatory system consists of:

  • heart
  • blood
  • blood vessels


  • constantly flows throughout the body
  • plasma – liquid part of blood
    • main component of blood
    • consists mostly of water
  • red blood cells
    • also known as erythrocytes
    • transport gases to and from the cells
    • hemoglobin – what makes the blood red, carries oxygen
  • white blood cells
    • also known as leukocytes
    • play a vital role in the immune system
  • platelets
    • also known as thrombocytes
    • smallest of the formed components of blood
    • help in blood clotting to stop or prevent bleeding

Blood vessels

  • vast networks of small tubes that carry blood throughout the body
  • arteries – carry oxygen-rich blood away from the heart
  • veins – carry deoxygenated blood back to the heart
  • capillaries – smallest blood vessels; serve as connection between arteries and veins

Two parts of the circulation:

  • pulmonary circulation – movement of deoxygenated blood from the heart and into the lungs
  • systemic circulation – movement of oxygenated blood from the heart to the different parts of the body


  • pumping organ of the body
  • average heartbeat – 60-100 beats per minute
  • atria (singular: atrium)
    • upper chambers of the heart
    • receive blood from parts of the body
  • ventricles
    • lower chambers of the heart
    • known as the pumping chambers
    • when they contract, blood is forced away from the heart
  • valves – overlapping tissue between atria and ventricles that allow blood to flow in only one direction

Nervous System

Nervous system

  • the body system that controls other parts of the body
  • receives signals from stimuli inside and outside of the body
  • main function: integrate and coordinate bodily activities
  • two main parts:
    • central nervous system (CNS) – brain and spinal cord
    • peripheral nervous system (PNS)


  • primary organ of the nervous system
  • cerebrum
    • largest part of the brain
    • receives sensory messages
    • center of emotions, consciousness, learning and voluntary movement
  • cerebellum
    • smaller, located beneath the cerebrum
    • coordinates involuntary and muscle action
    • responsible for ability to learn habits and develop skills
    • helps maintain sense of balance
  • brain stem
    • at the base of the brain
    • contains vital centers for autonomic functions

Spinal cord

  • cordlike material in the backbone

Peripheral nervous system

  • made up of nerves that branch off from the spinal cord and extend to all parts of the body
  • collects information from sense organs and transmits it to the CNS
  • deliver instructions from the CNS to the body parts that will act on them


  • the nerve cell
  • the functional unit of the nervous system
  • three parts: dendrites, cell body, axon
    • cell body
      • main component of the neuron
      • maintains the health of the neuron
    • dendrites
      • short fibers around the cell body
      • carry messages into the nerve cell
    • axon
      • long fiber of the neuron

Three types of neurons:

  • sensory neuron
    • typically has long dendrites and axons
    • carries messages from the receptor organs (skins, eyes, nose, ears, and tongue) to the nerve center
  • motor neuron
    • typically has short dendrites and long axons
    • receives information from the nerve centers and transmits it to the effector organs (muscles or glands)
  • interneurons
    • connect sensory neurons to motor neurons
    • found only in the central nervous system

Autonomic nervous system

  • controls or regulates the body’s internal environment, including the vital signs
  • vital signs
    • body temperature, pulse and respiration rate, and blood pressure
    • reflect the condition of your internal organs
  • two divisions:
    • sympathetic
    • parasympathetic
  • sympathetic and parasympathetic
    • produce opposing effects
    • both are directly involved in maintaining the normal functions of cells

Quarter 2 Module 3/4: Animals: Characteristics of Vertebrates


  • animals with backbone
  • can be:
    • viviparous – born live
    • oviparous – hatched from an egg
  • vertebrate groups:
    • mammals
    • fish
    • birds
    • amphibians
    • reptiles


  • warm-blooded
  • viviparous (born alive)
  • body covering: hair or fur
  • have mammary glands to feed their young with milk


  • cold-blooded
  • oviparous (hatched from eggs)
  • body covering: scales
  • breathe through gills
  • have tails and fins to help them swim


  • warm-blooded
  • oviparous (hatched from eggs)
  • body covering: feathers
  • have a pair of:
    • limbs for hopping
    • wings for flying (some have wings but can’t fly)
  • use their beak or bill to get food and protect themselves


  • cold-blooded
  • oviparous (hatched from eggs)
  • body covering: moist, scaleless skin
  • spend part of their lives in water and part on land
  • examples: salamander, newt, toad, caecilian


  • cold-blooded
  • oviparous (hatched from eggs)
  • body covering: dry, scaly skin
  • some have shells
  • examples: turtles, chameleon, snake, lizard, and gecko

Quarter 2 Module 5: Animals: Characteristics of Invertebrates


  • animals without backbones
  • 8 main groups (mnemonic: CAMP PANE):
    • arthropods
    • mollusks
    • echinoderms
    • poriferans
    • cnidarians
    • platyhelminthes
    • nematodes
    • annelids


  • segmented bodies with jointed legs
  • hardened outer skeleton (exoskeleton)
  • largest group in the animal kingdom
  • further classified based on how many pairs of legs
    • insects (class Insecta) – 3 pairs of legs
    • arachnids (class Arachnida) – 4 pairs of legs, ex. scorpions, spiders
    • crustaceans (class Crustacea) – 5 or more pairs of legs, ex. crabs, barnacles
    • class Chilopoda – 1 pair of legs per segment, ex. centipedes
    • class Diplopoda – 2 pairs of legs per segment, ex. millipedes


  • soft-bodied animals
  • usually have a hard shell (exceptions: squid, octopus)
  • examples: snails, clams, squids, octopus


  • marine animals
  • spiny endoskeleton
  • radial symmetry
  • tube feet
  • water vascular system
  • examples: sea stars, brittle stars, sea urchins, sea cucumber


  • sponges
  • pore-bearing animals
  • attach themselves to rocks or the sea floor


  • hollow-intestined animals (have a digestive cavity)
  • have just one body opening
  • have stinging cells called nematocysts
  • examples: jellyfish, corals, anemones, hydra

Platyhelminthes (flatworms)

  • flattened, elongated worm-like animals
  • examples: flatworms, flukes, tapeworms

Nematodes (roundworms)

  • elongated, unsegmented
  • worm-like or thread-like
  • can be free-living but mostly parasitic
  • examples: ascaris, vinegar eels, hookworms, pinworms

Annelids (segmented worms)

  • elongated, segmented with ringed appearance
  • have body segments that allow for specialization of tissues and for efficient movement
  • examples: earthworms, leeches, lugworms

Quarter 2 Module 6: Ecosystem: Tropical Rainforests, Coral Reefs, and Mangrove Swamps

Tropical Rainforests

Living things and non-living things interact with each other in an ecosystem.

In the forest ecosystem:

  • living things – ex. plants, animals
  • non-living things – ex. soil, air, humidity, water, sunlight

Layers of a rainforest:

  • emergent – trees that are 130 to 180 feet tall
  • canopy – trees that are 60 to 129 feet tall
  • understory
    • 59 feet and below
    • consists of trunks of canopy, shrubs, trees, and small plants
  • forest floor
    • plant life is thin because little sunlight gets through the thick canopy and understory and reaches the forest floor
    • home to animals like jaguars, tigers, and cassowaries
    • also contains fungi, insects, worms, and litter from taller trees

Producers and consumers

  • producers
    • provide food for the consumers
    • include trees, shrubs and other plant life
  • consumers – include:
    • herbivores – plant-eating animals
    • carnivores – flesh-eating animals

Feeding relationships

  • food chain – a series of feeding relationships that includes:
    • producer
    • series of consumers (primary, secondary, tertiary)
    • decomposers
  • food web – results from interconnected food chains

Interactions between organisms in a tropical rainforest ecosystem:

  • commensalism
    • the organisms live together without harming one another
    • example: orchids attached to the trunk of a tree – the orchids benefit, the tree is not harmed
  • mutualism
    • both organisms benefit in the relationship
    • example: insect sucks nectar, flower reproduces
  • competition
    • the organisms compete for survival
    • example: the grass, shrubs, flowers, and trees that grow together in one area compete for food, sunlight, soil, nutrients, and other needs
  • predation
    • one organism (predator) kills another organism (prey) for food
    • example: snake eats a rat for food

Coral Reefs

Coral reef

  • a marine biome that serves as a breeding ground for marine life
  • ecosystem composed of:
    • non-living things – ex. water, sand
    • living things – ex. fish, seagrass, corals, sponges and other marine animals

Organisms that interact with each other in a coral reef ecosystem:

  • producers – ex. seagrass
  • consumers – ex. sea turtles, crabs, manatees (dugong), fishes, other marine animals

Factors that contribute to coral reef formation:

  • temperature
  • light penetration
  • stable salinity
  • water movement

Categories of coral reefs:

  • fringing reefs – reefs that hug the shore of continents or islands
  • barrier reefs – reefs that stand between the open sea and a lagoon
  • coral atolls – reefs that enclose a lagoon

Interactions between organisms in a coral reef ecosystem:

  • commensalism
    • the organisms live together without harming one another
    • example: barnacles attached to the skin of turtles – the barnacles benefit, the turtle is not harmed
  • mutualism
    • both organisms benefit in the relationship
    • example: corals receive oxygen from the algae, the algae get protection from the corals
  • competition
    • the organisms compete for survival
    • example: fishes compete for source of food and space in the coral reef
  • predation
    • one organism (predator) kills another organism (prey) for food
    • example: a big fish eats a small fish – the big fish benefits, the small fish is harmed
  • parasitism
    • one organism (parasite) depends on another for food, protection, and reproduction
    • one organism benefits while the other is harmed (but not killed for food, unlike in predation)
    • example: worms in fish

Mangrove Swamps

The mangrove swamp ecosystem consists of:

  • non-living things – water, sand, mud, rocks, and sunlight
  • living things – a variety of marine and terrestrial life
    • mangrove plants – main organism that dominates the ecosystem
    • in the mangrove canopy – white heron (tagak) and other birds
    • attached to the trunk and lower branches of the mangroves – oysters, mussels
    • under the mangrove roots – fishes and crustaceans
    • migratory birds such as pelicans, spoon bills, and bald eagles
    • other animals such as saltwater crocodiles, monitor lizards, mudskippers, and crustaceans such as shrimps and crabs

Interactions between organisms in a mangrove ecosystem:

  • commensalism
    • barnacles and oysters attach themselves to the roots of mangroves
    • fish stay in the mangroves to grow and develop into mature fish
  • mutualism
    • crabs and mollusks that benefit from the mangroves also help break down plant litter in the ecosystem through grazing
  • predation
    • a white heron eating a fish

Importance of the mangrove ecosystem:

  • serve as breeding and nesting grounds of animal species
  • fish breed and nurse here before heading to the open ocean
  • important habitat of organisms
  • many animal species find protection and abundant food in this environment
  • natural barrier and flood defense – defend coastlines from flooding and erosion
  • important source of livelihood for people living in coastal areas

Practice Exam: Review Questions for First Quarter

1. How many bones does an adult human have?

a. 186

b. 196

c. 206

d. 256

2. The following are parts of the appendicular skeleton except _____.

a. carpals

b. ribs

c. tarsals

d. ulna

3. Which of the following pairings is incorrect?

a. femur – long bone

b. pinkie finger – short bone

c. skull – flat bone

d. spinal column – irregular bone

4. The outermost layer of the skin is the _____.

a. dermis

b. epidermis

c. extradermis

d. hypodermis

5. Which of the following is NOT a function of the integumentary system?

a. defense against pathogens

b. elimination of waste products

c. regulation of body temperature

d. none – all are correct

6. Digestion begins in the _____.

a. mouth

b. esophagus

c. stomach

d. small intestine

7. The rhythmic, wave-like movement of the digestive tract is called _____.

a. emesis

b. harmonic propulsion

c. peristalsis

d. traction

8. Final digestion and food absorption take place in the _____.

a. stomach

b. small intestine

c. large intestine

d. rectum

9. The part of the respiratory system that is also known as the windpipe is the _____.

a. bronchi

b. larynx

c. pharynx

d. trachea

10. The _____ are grape-like air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place.

a. alveoli

b. bronchi

c. bronchioles

d. diaphragm

11. The liquid part of the blood is called the _____.

a. blood corpuscles

b. hematocrit

c. hemoglobin

d. plasma

12. Leukocytes are also known as _____.

a. red blood cells

b. white blood cells

c. platelets

d. plasma

13. The blood vessels that carry deoxygenated blood back to the heart are the _____.

a. arteries

b. veins

c. capillaries

d. none of the above

14. How many chambers does the human heart have?

a. 2

b. 3

c. 4

d. 6

15. The system that controls and coordinates the activities of the body is the _____.

a. circulatory system

b. endocrine system

c. excretory system

d. nervous system

16. The following are parts of the brain except _____.

a. brain cord

b. brain stem

c. cerebellum

d. cerebrum

17. Which part of the nerve cell receives signals and passes them on to the main part of the cell?

a. axons

b. neurons

c. dendrites

d. cell bodies

18. Which statement is correct?

a. Sensory neurons carry messages from the brain to the effector organs.

b. Motor neurons carry messages from receptor organs to the brain.

c. Interneurons connect sensory and motor neurons in the peripheral nervous system.

d. None – all are incorrect

19. The division of the autonomic nervous system that produces opposing effects to the sympathetic nervous system is the _____.

a. parasympathetic nervous system

b. peripheral nervous system

c. somatic nervous system

d. unsympathetic nervous system

20. The following vertebrates are cold-blooded except _____.

a. amphibians

b. birds

c. fish

d. reptiles

21. Crocodiles are _____.

a. amphibians

b. cnidarians

c. flightless birds

d. reptiles

22. Which vertebrate – body covering pairing is incorrect?

a. amphibians – moist, scaly skin

b. fish – scales

c. mammals – hair or fur

d. reptiles – dry, scaly skin

23. Sponges belong to which group of invertebrates?

a. annelids

b. cnidarians

c. echinoderms

d. poriferans

24. Sea stars, sea urchins, and sea cucumbers are _____.

a. arthropods

b. coelenterates

c. echinoderms

d. mollusks

25. Which pairing is incorrect?

a. Crabs – arthropods

b. Snails – mollusks

c. Tapeworms – nematodes

d. None – all are correct

26. The topmost layer of the rainforest is the _____.

a. canopy

b. emergent

c. understory

d. forest floor

27. Pollinators such as bees drink nectar from flowers and, as they move around, carry pollen from the male part of the flower to the female part of the same or another flower. This is an example of which type of relationship?

a. commensalism

b. competition

c. mutualism

d. parasitism

28. The following are types of coral reef formations except _____.

a. atolls

b. barrier reefs

c. bleaching reefs

d. fringing reefs

29. Mudskippers are most likely found in which habitat?

a. coral reefs

b. mangrove swamps

c. tropical rainforests

d. tundra

30. Which is NOT a reason why mangrove swamps are important?

a. They serve as breeding and nesting grounds for many animal species.

b. They serve as natural barriers, protecting the coastline from flooding and erosion.

c. They are an important source of livelihood for people living in coastal areas.

d. None – all are correct


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