Life Cycles

Life Cycles

•Understand that all organisms have different life cycles

What is a life cycle?

• •The different stages an animal or plant goes through during its life.

• can you think of any examples?

Plant life cycles

• Plants are able to reproduce in two different ways - sexual reproduction and asexual reproduction.

  Sexual reproduction involves pollen from one flower fertilising the egg of another to produce a seed.

  Only one parent is needed in asexual reproduction and the offspring are exact copies.

Sexual reproduction in plants

Sexual reproduction in plants happens in a cycle-like pattern. Flowers come from seeds, and they create seeds too. All flowering plants go through the following life cycle.

Germination

This is the process by which a plant begins to grow from a seed. Roots form under the soil. The stem, leaves and flower emerge above the soil.

Pollination

Pollen produced by a flower is carried by insects or blown by the wind to another flower. This process is called pollination.

Fertilisation

When the pollen reaches another flower, it travels to the ovary where it fertilises the egg cells to make seeds. This process is called fertilisation.

Dispersal

These seeds are scattered by animals or the wind. This process is called dispersal. Some of the seeds will grow into new plants.

Asexual reproduction

• Some plants can also reproduce without an egg cell being fertilised to produce a seed. Instead, these plants produce an identical copy of themselves.

• Some plants produce bulbs, like daffodils and snowdrops. Others, like potatoes produce tubers. These sit under the soil and develop into new plants the next year.

Multiple Choice

What happens first in a flowering plant's life cycle? ___ - pollination - fertilisation - seed dispersal

• nectar

• spores

• germination

Multiple Choice

Why are flowers important in a plant's life cycle?

• they produce seeds

• they are given as gifts

• they make food

Multiple Choice

What is it called when a plant first starts to grow from a seed?

• pollination

• germination

• growing

Multiple Choice

What are the two parts of a flower a bee moves the pollen between?

• petal and nectar

• leaf and seed

• stigma and stamen

Multiple Choice

Which of these is NOT a way flowers use to scatter their seeds into the world?

• animal droppings and fur

• wind and water

• flapping their leaves

Human Life Cycle

• •The human life cycle has six main stages: 

• •foetus, baby, child, teenager, adult and being elderly. 

1. Foetus

At this time, a baby is growing inside its mum's uterus.

2. Baby

A baby is born after spending nine months inside the womb.

3. Childhood

At this stage, you learn to walk and talk.

4. Adolescence

Children become teenagers.

5. Adulthood

Your body is fully developed.

6. Old age

The last stage in the life cycle of a human.

Multiple Choice

What is the missing stage in the human life cycle? foetus - baby - childhood - ___ - adulthood - old age

• infant

• adolesence

• OAP

Multiple Choice

During the ___ stage, a baby is growing inside the mother’s womb.

• baby

• adolescence

• foetus

Multiple Choice

At what stage of the life cycle does a human learn to walk and talk?

• baby

• child

• adult

Multiple Choice

What is it called when a teenager’s body starts changing?

• pollination

• foetus

• puberty

Gestation period: 

• •The period of development during the carrying of an embryo or foetus inside viviparous animals

• What does viviparous mean?

Viviparous:

An animal that is viviparous gives birth to developed live young.

Gestation periods

• All viviparous animals have different gestation periods

• The development time depends somewhat on the size of the animal

• Larger animals tend to have longer gestation periods, but usually only have one baby at a time

• Smaller animals have a much shorter gestation period and usually have multiple babies.

• WHY DO YOU THINK THIS IS?

1. ELEPHANTS: 640-660 DAYS

• Elephants are pregnant for a long time. Like really, really long. At an average of 95 weeks, the gestation period is more than double the length of a human pregnancy, female elephants don't often have more than four offspring during their lifetimes. 

• 
  

GIRAFFE: 14-15 MONTHS

• Baby giraffes can weigh more than 150 pounds and can be around 6 feet tall. Giraffes give birth standing up, so it's pretty normal for a baby to fall 6 feet to the ground.

Danger

The lives of both of the previous babies depend on them being able to walk then run within minutes of birth

WHY?

Opossum: 11-13 days

• An average litter consists of 8-9 infants. The infants are so small at birth that 20 could fit into a teaspoon and weigh approximately 0.13 grams. At birth, the infants must make a difficult journey from the birth canal into the pouch, latch onto a teat, and continue their development.

Hamsters: gestation lasts from 16 to 22 days,

• Normal litters contain 6 to 8 pups, and offspring are weaned after about 21 to 28 days. The pups are hairless and their eyes and ears are closed; however, pups have their front teeth (incisors) at birth. 

Open Ended

Why do you think smaller mammals have so many offspring in one litter?

Human Gestation

• Human gestation lasts for roughly 280 days - (40 weeks) (9 months)

• Usually 1 child is born

• Twins and triplets are not unusual.

Longest gestation period

Can you guess which animal has the longest gestation period?

How long do you think it lasts?

Open Ended

Which animal do you think has the longest gestation period and how long do you think it lasts?

Frill shark: 3.5 - 4 Years!!

• Although it has no distinct breeding season, the frilled shark produce a litter of 2–15 shark pups.

• The frill shark are ovoviviparous - eggs hatch inside the mother and live young are born.

Multiple Choice

What does gestation period mean?

• development time before birth

• how long birth lasts

• how many offspring an organism has

Multiple Choice

How long is human gestation?

• 10 months

• 9 months

• 6 weeks

• 450 days

Multiple Choice

What does viviparous mean?

• hatched from eggs outside of the body

• eggs hatch inside the mother then live young are born

• live young are born, no egg stage

Multiple Choice

What does gestation period mean?

• development time before birth

• how long birth lasts

• how many offspring an organism has

Metamorphosis:

• Amphibians, like frogs and newts, have a slightly more complicated life cycle. 

• They undergo a metamorphosis (a big change):

The stages:

• they are born (either alive from their mother or hatched from eggs)

• they spend their childhood under water, breathing with gills

• they grow into adults and move to the land, breathing with lungs

Complete Metamorphosis: Insects

• egg:  unborn stage

• larva:  young stage -- this is when most of the feeding is done.  (they usually look like worms)

• pupa: inactive (no feeding) stage between larva and adult stages.   

• adult: final, breeding stage.(they usually grow wings)

Incomplete metamorphosis

About 10% of insects go through an incomplete metamorphosis. They do not have a pupal form -- these include dragonflies, grasshoppers and cockroaches.

These insects have three stages in their life cycle:

• egg:  unborn stage.

• nymph:  young stage -- this is when most of the feeding is done.

• adult:  final, breeding stage - including wings.

Find examples of metamorphosis

Draw out the stages in your exercise book. Carefully label each stage and be ready to share with the class.