Growth and development title Growth and development

21.1 What are growth and development? content 21.1 What are growth and development? 21.2 How to measure growth changes? 21.3 Growth and development in plants 21.4 Growth and development in animals

21.1 What are growth and development? zygote adult grows develops

by mitotic cell division Growth a non-reversible increase in size and weight of an organism by mitotic cell division results from cell division increase in cell number increase in cell volume cell enlargement

second mitotic cell division first mitotic cell division Growth cell division second mitotic cell division repeated divisions first mitotic cell division zygote daughter cells a ball of cells cell enlargement

forming specialized cells to perform different functions Development an increase in complexity of the body organization results from forming specialized cells to perform different functions differentiation of cells into different types of cells forming tissues, organs and systems

Development cell differentiation a cell in this region differentiates into e.g. a red blood cell a cell in this region differentiates into e.g. a nerve cell (newly formed red blood cell contains a nucleus) cell differentiation (mature red blood cells in humans contain no nucleus)

similar cells group together tissue other tissue(s) tissue different tissues group together Three levels of structural organization are present in an organism other organ(s) organ different organs group together system

21.2 How to measure growth changes? By measuring : Dry mass or dry weight Fresh mass or fresh weight Size Choice of quantity depends on the type of organism.

Dry mass or dry weight the mass/weight with water removed commonly used for plants

Dry mass or dry weight Advantage Disadvantages Accurate measurement of the amount of organic matter in an organism Time-consuming Organisms killed, so growth of the same specimen cannot be measured continuously Large number of specimens needed

Greater variation due to changes in environment or behaviour Fresh mass or fresh weight the mass without body water removed Advantages Disadvantage Organism remains alive growth can be measured continuously Greater variation due to changes in environment or behaviour Easy and quick

Size measurement of length/height, surface area or volume for structures having a regular shape for structures that grow mainly by elongation for flat structures

Size Advantages Disadvantage Organism remains alive growth can be measured continuously Size is measured in one dimension, growth in other dimensions cannot be taken into account Relatively easy and convenient

Size is measured in one dimension, growth in other dimensions cannot be taken into account

21.3 Growth and development in plants cells that can carry out mitosis throughout the plant’s life Mitotic cell division of a plant occurs in regions which have meristems e.g. apical meristem at the tip of a shoot/root

Growth and development at the root tip Region of cell division the cells divide mitotically to produce new cells the cells formed earlier will be pushed further behind the root tip region of cell division dense cytoplasm with no vacuole root cap apical meristem

Growth and development at the root tip Region of elongation the cells enlarge by taking in water region of elongation smaller vacuole thinner cell wall

Growth and development at the root tip xylem vessel larger vacuole region of differentiation thicker cell wall root hair Region of differentiation the cells become specialized for performing different functions

Measuring growth of the main root of a seedling using ink Carry out Practical 21.1 Measuring growth of the main root of a seedling using ink

Growth and development at the shoot tip Growth in shoots is similar to that in roots. young leaf region of cell division (apical meristem) region of elongation region of differentiation

Growth curve of an annual plant plant which lives for only one growing season 5 10 15 20 25 30 40 50 time (weeks) dry mass (g) 3 stages Dry mass decreases during early stage of germination because the stored organic food is respired to provide energy for growth.

rate of photosynthesis Growth curve of an annual plant 5 10 15 20 25 30 40 50 time (weeks) dry mass (g) Dry mass increases once the leaves are produced. rate of photosynthesis rate of respiration > food produced food consumed >

Growth curve of an annual plant death 5 10 15 20 25 30 40 50 time (weeks) dry mass (g) Dry mass decreases due to dispersal of fruits and seeds.

21.4 Growth and development in animals Plants Animals Cell division occurs only in regions that have meristem. Cell division occurs in all parts of the body.

Growth curve of a human 5 stages infancy rapid growth rate childhood adolescence rapid growth rate adult stage old stage Growth curve of a human

Change in body proportion from infancy to puberty Growth curve of a human with Different body parts Different growth rates For example: Relative size of head _________ with age. decreases Infancy Childhood Puberty Infancy Childhood Puberty Change in body proportion from infancy to puberty

Change in body proportion from infancy to puberty Growth curve of a human with Different body parts Different growth rates For example: Relative length of trunk ________________ with age. remains the same Infancy Childhood Puberty Infancy Childhood Puberty Change in body proportion from infancy to puberty

Change in body proportion from infancy to puberty Growth curve of a human with Different body parts Different growth rates For example: Relative length of legs _________ with age. increases Infancy Childhood Puberty Infancy Childhood Puberty Note that proportions change at different rates in boys and in girls. Change in body proportion from infancy to puberty

Different organs also grow at different rates. Growth curve of a human Different organs also grow at different rates. 5 10 15 20 30 40 50 60 70 80 90 100 relative rate of growth age (years) brain whole body reproductive organs

Concept diagram Growth of organism size weight cell division is the non-reversible increase in involves size weight cell division cell enlargement by mitotic cell division

Development of an organism Concept diagram Development of an organism results from cell differentiation leads to increase in variety of cell types complexity of cells form form tissues organs form systems