IB MYP 4-5 Biology-Life Cycles- Study Notes - New Syllabus
IB MYP 4-5 Biology-Homeostasis- Study Notes – New syllabus
IB MYP 4-5 Biology-Homeostasis- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Stages of development in organisms
- Metamorphosis (complete vs incomplete)
- Human life cycle from zygote to adult
Life Cycles – Stages of Development in Organisms
What is a Life Cycle?
A life cycle is the series of stages an organism goes through from birth to growth, reproduction, and finally death.
Every living thing – plants, animals, insects, and humans – has a life cycle, though the stages may differ in form or duration.
Key Idea: Life cycle = birth → growth → reproduction → death
Why Are Life Cycles Important?
- Help organisms grow and reproduce
- Show how life continues across generations
- Help us study survival and changes in species
Main Stages of a Life Cycle
Birth or Beginning
Life begins – born, hatches, or sprouts.
- A chick hatches from an egg
- A baby is born
- A seed germinates into a plant
Growth and Development
Organism grows, changes, and learns to survive.
- Child becomes a teenager
- Caterpillar eats and grows
- Seedling develops leaves and roots
Maturity / Adulthood
Organism can now reproduce.
- Butterfly ready to lay eggs
- Plant produces seeds
- Lion can have cubs
Reproduction
Organism creates offspring so the cycle continues.
Note:
Reproduction can be:
– Sexual (2 parents – humans, birds)
– Asexual (1 parent – bacteria, some plants)
Ageing and Death
Eventually, the organism ages and dies – but leaves behind new life through reproduction.
Different Types of Life Cycles
1. Simple Life Cycle
- Baby looks like a smaller version of adult
- Grows bigger with time
- Examples: Humans, birds, dogs, fish
2. Complex Life Cycle (with Metamorphosis)
- Baby looks very different from adult
- Goes through dramatic body changes
Butterfly Life Cycle:
- Egg → Caterpillar → Pupa (chrysalis) → Adult Butterfly
Frog Life Cycle:
- Egg → Tadpole → Grows Legs → Adult Frog
Plant Life Cycle
- Seed → Germination → Seedling → Adult Plant
- Flowering → Pollination → Fertilization
- Seed formation → Death → New seed grows
Remember: Metamorphosis = Big change in body structure
Every organism grows, develops, and reproduces – but life cycles differ
Life cycles help us understand biology, farming, and conservation
Summary – Life Cycles at a Glance
- Life cycle = birth → growth → reproduction → death
- Two types: Simple (like humans), Complex (like frogs, butterflies)
- Plants have their own unique stages
- Understanding life cycles helps in biology, farming, conservation
Metamorphosis – Complete vs Incomplete
What is Metamorphosis?
Metamorphosis is a biological process in which an organism undergoes major changes in its body structure as it grows from a young stage to an adult. It’s common in many insects and amphibians.
Why Metamorphosis Happens:
- Helps the organism adapt to different environments at each stage
- Avoids competition for food between young and adults
- Prepares the body for reproduction
Two Types of Metamorphosis
1. Complete Metamorphosis (Holometabolous)
Definition: The young and adult look completely different. The organism goes through four distinct stages.
Four Stages:
- Egg: The life begins
- Larva: Active stage that eats and grows (e.g., caterpillar, maggot)
- Pupa: Resting stage where major changes happen (inside cocoon)
- Adult: Final form (can reproduce)
Examples: Butterfly, Housefly, Beetle, Mosquito
Key Features:
- Big transformation
- Larva and adult live in different habitats
- Larva can’t reproduce
Life Cycle Example: Butterfly
- Egg
- Caterpillar (larva) – eats a lot
- Chrysalis (pupa) – transformation
- Butterfly (adult) – lays eggs
2. Incomplete Metamorphosis (Hemimetabolous)
Definition: The young (called nymph) looks like a smaller version of the adult, but without wings or reproductive organs.
Three Stages:
- Egg
- Nymph: Grows in size, molts (sheds skin)
- Adult: Grows wings and can reproduce
Examples: Grasshopper, Cockroach, Dragonfly, Termite
Key Features:
- No pupa stage
- Nymph and adult look similar
- Changes are gradual (not dramatic)
Life Cycle Example: Grasshopper
- Egg
- Nymph – eats and molts several times
- Adult – fully grown with wings
Complete vs Incomplete Metamorphosis
| Feature | Complete Metamorphosis | Incomplete Metamorphosis |
|---|---|---|
| Number of stages | 4 (egg, larva, pupa, adult) | 3 (egg, nymph, adult) |
| Appearance of young | Very different from adult | Similar to adult |
| Pupa stage present? | Yes | No |
| Example organisms | Butterfly, beetle, fly | Grasshopper, cockroach, dragonfly |
| Growth pattern | Sudden change in pupa stage | Gradual molting |
Summary:
- Metamorphosis = transformation during an organism’s life cycle
- Complete = 4 stages, major body change (e.g., butterfly)
- Incomplete = 3 stages, young looks like adult (e.g., grasshopper)
- Helps reduce competition and adapt to different habitats
Human Life Cycle – From Zygote to Adult
What is the Human Life Cycle?
The human life cycle describes the stages a human pass through from a single fertilized cell (zygote) to adulthood and old age. It includes growth, development, and reproduction.
Main Stages in the Human Life Cycle:
1. Zygote – The First Cell
- A zygote forms when sperm fertilizes an egg. It contains all the genetic material to become a human.
- Zygote = fertilized egg
2. Embryo – Early Development
- The zygote divides and implants in the uterus. Organs like brain and heart begin forming.
- Weeks 1–8 = embryonic stage
3. Fetus – Body Formation
- From week 9 to birth, the baby is called a fetus. It develops limbs, organs, and facial features.
- Protected in amniotic sac, nourished by placenta
4. Birth (Infancy)
- Baby is born around 9 months. Begins breathing, feeding, and reacting to touch.
- Infancy: Birth to 2 years
5. Childhood
- From 2 to ~12 years. Growth in height, brain, and independence. Starts school and social learning.
- Develops motor and language skills
6. Adolescence (Teenage)
- Puberty stage from 12–18 years. Hormonal, physical, emotional, and social changes.
- Development of reasoning and identity
7. Adulthood
- Begins ~18 years. Full physical maturity. Capable of reproduction and responsibility.
- Longest life stage
8. Old Age and Death
- Muscles weaken, senses decline, and memory may fade. Death is a natural end to the cycle.
- Life continues through the next generation
Summary Table: Human Life Cycle Stages
| Stage | Key Features |
|---|---|
| Zygote | Fertilized egg, one cell |
| Embryo | Early development, organs begin forming |
| Fetus | Growth and body formation |
| Infant | Learns to breathe, move, feed |
| Child | Steady growth, learning and skills |
| Teen (Adolescent) | Puberty, emotional and physical changes |
| Adult | Fully developed, able to reproduce |
| Old Age | Aging, memory and strength decline |
Real-Life Biology Connection:
- Ultrasound tracks fetal development
- DNA from sperm and egg combine in zygote
- Hormones like estrogen/testosterone cause puberty
Final Recap:
- Human life starts as a zygote and continues through stages: embryo, fetus, infant, child, teen, adult, old age.
- Each stage involves physical, mental, and emotional changes.
- This cycle allows life to continue across generations.