What is Measurement of Growth?
Growth can be estimated by measuring some aspect of the organism such as height, weight, volume and length over a specified period of time. The measurements so obtained if plotted against time result into a growth curve.
The following results were obtained from a study of germination and early growth of maize.
The grains were sown in soil in a greenhouse and.at two-day intervals. Samples were taken, oven dried and weighed. See table.
Plot a graph of dry mass of embryo against time after sowing.
Describe the shape of the graph.
For most organisms when the measurements are plotted they give an S-shaped graph called a sigmoid curve such as in figure. This pattern is due to the fact that growth tends to be slow at first and then speeds up and finally slows down as adult size is reached. A sigmoid curve may therefore be divided into four parts.
Lag phase (slow growth)
This is the initial phase during which little growth occurs. The growth rate is slow due to various factors namely:
Exponential phase (log phase)
This is the second phase during which growth is rapid or proceeds exponentially. During this phase the rate of growth is at its maximum and at any point, the rate of growth is proportional to the amount of material or numbers of cells of the organism already present.
This rapid growth is due to:
This is the third phase during which time growth becomes limited as a result of the effect of some internal or external factors, or the interaction of both.
The slow growth is due to:
Plateau (stationary) phase
This is the phase which marks the period where overall growth has ceased and the parameters under consideration remain constant.
This is due to the fact that:
PRACTICAL ACTIVITY I: PROJECT
To measure the growth of a plant
Small plots/boxes, meter rule and seeds of beans (or green grams, peas, maize),
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Growth is a characteristic feature of all living organisms.
Most multi cellular organisms start life as a single cell and gradually grow into complex organisms with many cells. This involves multiplication of cells through the process of cell division.
This quantitative permanent increase in size of an organism is referred to as growth.
For growth to take place the following aspects occur
Reproduction in Plants and Animals Practical Activities
Examining the stages of mitosis
To examine spores on sori of ferns
Dispersal of fruits and seeds
Sexually transmitted infections (STl)
Advantages of Reproduction Asexual
Disadvantages of asexual reproduction
Advantages of sexual reproduction
Disadvantages of sexual reproduction
ROLE OF PLACENTA
The placenta facilitates the transfer of nutrients from maternal blood to foetus.
Placenta facilitates the removal of nitrogenous wastes from the foetus' blood to maternal blood.
Oxygen from the maternal blood diffuses into the foetal blood while carbon (IV) oxide from foetal blood diffuse into maternal blood.
Production of hormones
Placenta produces progesterone and oestrogen.
The period between conception and birth is called gestation.
In humans gestation takes nine months (40 weeks).
The embryo differentiates into tissues and organs during this period.
Week 1 to 3:
Zygote divides to form blastocyst.
Implantation takes place.
The three germ layers form endoderm, mesoderm and ectoderm.
Nervous system starts to form.
Week 4 to 7:
Development of circulating and digestive systems.
Further development of nervous system, formation of sensory organs,
All major internal organs are developed.
At week 5, heartbeat starts.
Week 8 to 24:
All organs well developed including sex organs.
Hair, finger and toe nails grow.
Foetus move and eyelids open.
Week 25- 30:
The fully developed foetus responds to touch and noises and moves vigorously.
The head turns and faces downwards ready for birth.
Foetus increases in size.
Reproduction in Animals
Reproduction in Humans
Structure of female reproduction system,
The female reproduction system consist of the following: Ovaries
Structure of male reproductive system
The male reproductive system consists of the following:
Fertilisation in Animals