Growth and DevelopmentL.O.s

Describe how growth can be measured and interpret data on increases in mass.

Describe and explain why plant growth is different to animal growth.

Explain the advantages and disadvantages of the different methods of measuring growth.– Starter What is the difference between

animal and plant growth?

Bacteria Cell

Bacteria Cells Bacteria are usually made from 1 cell.

Bacteria cells are much smaller and simpler than animal and plant cells.

They still have DNA but no nucleus.

The DNA is found in the cytoplasm. Mitochondria and chloroplasts are also missing from bacterial cells.

Animal and Plant Growth

Key Words

cell differentiation • cell enlargement • dry mass • finite size • growth curve • meristems • wet mass

Growth and Development

Growth = Cell multiplication +

Cell enlargement

Growth When plants and animals grow, cells need to

divide and change into specialised cells. For example, nerve cells and bone cells.

The specialised cells can carry out different jobs.

When a cell changes to become specialised the process is called cell differentiation.

Stem Cells A fertilised egg cell contains a group of undifferentiated cells

called stem cells.

Stem cells have the same simple cell structure. They divide and then differentiate (change) to form all the different specialised cells in the body.

As the embryo grows all the specialised cells form tissues and organs.

A few stem cells are found in the adult body. Bone marrow contains stem cells that turn into different types of blood cells.

Stem Cell Research Scientists have found ways to make stem

cells develop into other specialised cells. They can be taken from embryos and used to treat medical conditions.

Many people object to stem cell research because it can involve human embryos. Scientists use embryo stem cells because they are easier to grow than adult stem cells.

Growth in Animals

Only grow in the early stages of their lives.

The whole animal grows.

Tend to grow a certain size then stop.

Growth is by cell division only.

Cells lose the ability to differentiate.

Growth in Plants Keep on growing all their life.

Only specialised parts of the plant continue to grow.

Cell division takes place in special areas called meristems. Meristems are found at the tips of the roots and shoots.

Plants increase in height because their cells get larger rather than just cell division.

Cells retain their ability to differentiate.

Measuring Growth Growth can be measured by

recording:

Increases in height Increases in mass

Plants have an S-shaped growth curve. There are 3 phases on a growth curve.

Phase 1: growth starts slow. Phase 2: growth speeds up. Phase 3: growth slows down.

Mass and Growth The growth of plants can be measured by measuring

the increase in mass. This can be done in two ways:

Measuring the Wet Mass The mass of the whole organism is measured. This can be done when the organism is alive.

Measuring the Dry Mass Done when all the water has been removed. This can only be done on dead organisms. This is more accurate because the water content can

change depending on conditions.

Measuring Mass

Method Advantages Disadvantages

Length Quick and easy method

Organism may increase in size but length may not change

Wet mass Live organism can be measured

Water content can change

Dry mass More accurate method

Cannot measure live organism

Growth in Humans

Humans are different than plants, they normally have two phases of rapid growth:

- Phase 1: rapid growth just after birth.

- Phase 2: rapid growth during adolescence.

Stages in Human Growth

There are 5 stages in human growth:

• Infancy• Childhood• Adolescence

(puberty)• Adulthood (maturity)• Old age (elderly)

Gestation

This is the length of time from fertilisation to birth.

The larger the animal is the longer the gestation tends to be. This is because the animal needs time to develop enough to survive outside the uterus.

Growth Charts Look at any class picture, and you’ll see kids of the same age in

all shapes and sizes. Some kids look tiny next to their peers, while others literally stand head and shoulders above their classmates.

As easy as it is to make these comparisons and to draw conclusions about what you see, the reality is that kids grow at their own pace. Big, small, tall, short – there is a wide range of healthy shapes and sizes among children.

Genetics, gender, nutrition, physical activity, health problems, environment, hormones and lifestyle factors like nutrition and physical activity all influence a child’s height and weight and many of these factors can widely from family to family.

A doctor uses growth charts to help answer how a person’s height and weight are ‘normal’.

Growth Curves – Birth to 36 Months – Boys

Growth charts are a standard part of any check-up, and they show health care providers how kids are growing compared with other kids of the same age and gender.

They also allow doctors and nurses to see the pattern of kids’ height and weight gain over time, and whether they’re developing proportionately.

Growth Curves – Birth to 36 Months – Girls

Percentiles are measurements that show where a child is compared with others. On the growth charts, the percentiles are shown as lines drawn in curve patterns.

Up until the time babies are 36 months old, doctors measure weight, length and the head circumference – brain development.

Percentiles When doctors plot a child’s weight and height on the

chart, they see which percentile line those measurements land on.

The higher the percentile number, the bigger a child is compared with other kids of the same age and gender, whether it’s for height or weight.

The lower the percentile, the smaller the child is.

For example, if a 4 year old boy’s weight is in the 10th percentile, that means that 10% of boys that age weight less than he does and 90% of 4 year old boys weigh more.

Growth Problems

A baby’s weight and head size are important to measure. Results can be plotted on a graph and be compared with graphs showing expected growth.

Detected Problems

Poor Weight Gain – can indicate problems with the baby’s digestive system.

Large Head Size – can indicate fluid collection on the brain or the separate bones not fusing together.

Answers

Q8a 14–16 • Q8b Growth stops • Q8c Approx. 9–13 • Q9a 2 • Q9b Lack of space, water or minerals • Q10 To measure dry mass you need to kill the organism • Q11 Growth is all over the human body but mainly in the meristems of the tree, tree continues to grow humans reach a finite size • Q12 May get rounder but not increase in length • Q13 Water content varies • Q14 Place it in an oven to dry out, record mass before and after drying

Questions

1. How can growth be measured?2. How do plants grow?3. How do animals grow?4. What are the three phases of growth in plants?5. Which growth phase in plants is the fastest?6. Where does growth mainly occur in plants?7. When does growth occur most in humans?8. Human growth cannot be measured by using dry mass.

Why?9. Describe one way the pattern in human growth is

different to that of an apple tree.10. Why does a human foetus’ head grow faster than the rest

of its body?