Sunday, May 17, 2015

Sexual Reproduction in Humans

Male Reproductive System consists of:

  - produce sperm + hormones
  - under the influence of pituitary gonadotrophins, FSH +LH
  - contains scrotum 
  - kept 2 °C <normal body temperature
  - optimal for sperm production (spermatogenesis).

2. Ducts:
  - vasa efferentia + vas deferens
  - transport sperm to urethra
3. Glands:
  - prostate gland, Cowper’s gland, seminal vesicles
  - contribute fluid to semen.

4. Sperm (in seminal fluid)
  - discharged from body thru penis ( intromittent organ).

5. Each testis:
  - consists of about a thousand seminiferous tubules.

6. Each tubule:
  - lined by germinal epithelium
  - which divides to give rise to sperm
  - + two months.

1. Interstitial cells:
   - between seminiferous tubules
   - contain Leydig cells 
   - produce testosterone
   - influence of LH (in pituitary gland).
2. Testosterone:
   - stimulates development + maintenance of male secondary sexual
     characteristics + accessory sex organs.
3. Spermatogenesis:
    - starts at puberty
    - when FSH stimulates series of cell divisions
    - of germinal epithelium
    - of seminiferous tubules.
4. Spermatozoan cell:
    - cytoplasm disappeared during development.

5. Acrosome:
    - large lysosome
    - enzymes to digest outer membranes of the egg (female gamete)
6. Mitochondria - provide energy for locomotional flagella movement.

Human female reproductive system consists of:

1. Pair of ovaries:
   - which produce ova
   - carried by Fallopian tubes (oviductus)
   - to uterus.

2. cervix - muscular ring at outer end of uterus.

3. vagina – opening to outside of body.


1. At birth:
   - ovaries contain about two million follicles
   - which started to divide by meiosis,
   - but stopped at prophase I (primary oocytes).
   - subsequent development at monthly intervals (menstrual cycle).
2. Oogenesis is regulated by the pituitary hormones FSH + LH
3. Ovulation + development of secondary sexual characteristics
   + uterine changes in preparation for implantation of a fertilised egg
   - controlled by the ovarian hormones (oestrogen + progesterone).
4. Fertilisation:
   - occurs in the Fallopian tubes
   - and the zygote is transported to the uterus
   - by the action of cilia lining.
5. Development of the zygote + embryo is viviparous

Thursday, November 27, 2014


1. Growth is a:
  • characteristic of all living organisms.
  • permanent irreversible increase in size of an organism
  • due to increase in its dry mass.
  • continue throughout the life of an organism (eg: woody perennial plants)
  • may cease when organism reach maturity (eg: man  or other mammals)
2. Result is irresversible:
  • increase in volume of cytoplasm
  • Increase in number of cells
  • increase in differentiation of cells
3. Growth in unicellular organisms:

  • reaches certain size – divide to form two separate cells
  • size limited - due to distance of cell over which a nucleus can exert its controlling influence.
  • division - results in growth of populations.
4. Growth in multicellular organisms:
  • originate from a single cell (the zygote)
  • cell division – increase in number of new cells produced by mitosis
  • cell expansion (cell enlargement) – increase in size, volume + mass (due to assimilation of food materials +  metabolism)
  • cell differentiation:
           i. cells undergo progressive changes in metabolic activities:
               – lead to changes in cell structures
               – produce diff specialized cells/tissues for dif functions
           ii. in higher animals:
                – produce tissues (epithelial tissue, nervous tissue, muscle tissue + connective tissue)
           iii. in higher plants:
                – produces tissues (meristematic tissue, ground tissue +  vascular tissue).
5.   Morphogenesis
      a. result from:
  • development (growth+ differentiation) of overall form of organs
  • formation of multicellular organism
      b. cell differentiation cause by:
  • differential expression of genes.
  • certain metabolites activate/repress gene in dif. cells.
  • some hormones are able to switch genes on/off (help to determine overall pattern of development)


A.    External factors affecting the rate of growth in plants are:

  1. light (intensity, wavelength and photoperiod) – affects photosynthesis, photomorphogenesis, meristemic activities and flowering.
  2. Temperature which affects enzyme activities.
  3. Oxygen – require for aerobic respiration and seed germination.
  4. Carbon dioxide – for photosynthesis, synthesis of organic molecules.
  5. Water – essential for many metabolic processes (photosynthesis, seed germination, transportation of mineral salts/soluble organic material, vacuolation, maintenance of plant cell turgidity
  6. Relative humidity of atm – affects rate of transpiration.
  7. Minerals (K+, Na+, Ca2+, NO3+) for plant metabolism/growth/development.
  8. Gravity – affects distribution of growth regulators for geotropism
  9. Seasonal influences – affect dormancy, abscission, reproduction and photoperiodism
  10. Biotic factors -pathogen-caused plant diseases, intraspecific and interspecific competition for space, sunlight, water and mineral salt).
B. Internal factors are:

  1. Genotype of the plant – determines the synthesis of specific proteins and enzymes, the type of metabolism and size.
  2. presence and absence of growth regulators/plant hormones (auxins, gibberellins, cytokinins, absciccis acid, ethene)
 C. Animal growth + development are controlled mainly by:

  1. Genotype of the animal
  2. Animal hormones (thyroxine and somathrophin).
  3. Environmental conditions (lights intensity and photoperiod, temperature, oxygen, availability of water and seasonal influences.
  4. Biotic factors.

Advantages + disadvantages
Height and length
·      easy + quick to measure.
·      growth can be measured continually
·       only measures the length in one dimension + does not take into account growth in other directions.
·       An organism not increasing in height - may continue to grow in girth or grow sideways (as in plant)
Surface area
·      more accurate measurement.
·      eg: surface area of a leaf attached to a plant can be measure at regular intervals over a period of time.
·       Dif. + impractical to carry out if the organism is irregular in shape.
·       It’s assumed that plant growth is directly proportional to the increase in the surface area of its leaves.
Volume, size
·       Suitable for measuring organisms that are spherical or cylindrical in shape.
·       Living organisms are rarely exactly spherical and cylindrical in shape
·       Not accurate measurement.
·       Dif. to carry out – complicated calculation for organism with irregular shape.
Dry mass
·       More accurate measurement of the organic materials (protein present in the body.
·       Water has to be removed by drying the organism.
·       This kills the organism, so continuous growth of the same organism cannot be measured
·       Have to use a large number of individuals from the same population which have similar age and size.
·       Dif. plants used may have dif, growth rates.
Wet mass or fresh mass
·      Easy to measure
·      No need to kill the organism.
·      Growth can be measured continuously as repetitive measurements can be carried out.
·       Measurement may be inaccurate due to fluctuations in water content in the body.
·       May be more suitable for measuring growth in animals but not for a living tree.