Observe the pictures related to the reproduction of plants.Is the sprouting of sapling from a seed the same as the growthof new plants from leaves? Why?Discuss and write down your inferences in the science diary.There are different modes of reproduction in nature to producenew generation. Some examples are given below. Collect moreinformation about different types of reproduction and writethem down in your science diary

Flowers are the sex organs in plants.Collect flowers from the surroundings and observe themwith the help of a hand lens. Identify the parts that takepart in reproduction and complete the illustration givenbelow

 Pollination is the transfer of pollen grains to the stigmaof the flowers. What is the change that happens to thepollen grain after fertilization?Observe the figure.

Let us observe through a simple experiment the growthof the pollen tube from the pollen after pollination.Plan the experiment according to the hints given in theillustration. Prepare a note on the experiment and recordit in the science diary

  Stages of the experiment

 Basic Science VIII199Stage 1Collect anthers from any ofthe flowers available in thelocality. eg: lily, Mexican lilac(sheemakonna), hibiscus.Stage 2Place the pollen grains ona glass slide. Add 2 or 3drops of sugar solution to it.Then place a cover glassover it.Stage 3Observe through amicroscope after 3 to4 hours.

 Did you observe the growth of the pollen tube? On the basis of theindicators, discuss the given notes and figure on fertilization in plants.Note down the inferences in your science diary.

 

Indicators

 Formation of male gametes.Formation of embryo.Formation of endosperm and its function

 Reproduction in human beingsIn higher organisms including human beings specific organ system isdeveloped to produce gametes. Analyse the illustration and notesgiven below and write the inferences in your science diary.

 SpermSperm is the male gamete. It is motile andmicroscopic. The sperm has a head, middlepiece and a tail. They move with the helpof the tail. Mitochondria, present in themiddle piece, provides the energy formovement. Nucleus that contains paternalchromosomes is seen in the head.Sperms are formed inside a pair of testeslocated in the scrotal sac outside the

 

 abdominal cavity. Testis also produces testosterone, the male sexhormone. Temperature less than the body temperature (35-36oC) isfavourable for the formation of sperms. The scrotal sac helps tomaintain this temperature. Sperms along with the secretion of glandsincluding the prostate gland reaches the penis and is secretedoutside. This process is called insemination.

 ndicatorsCharacteristics of sperms.Location of testes and the production of sperms.Importance of glands.

 OvumOvum is the female gamete. It is larger thana sperm. Ovum is non motile. Specialisedprotective layers are seen outside the cellmembrane of the ovum

 A pair of ovaries situated in the abdominalcavity produces ova, and the female sexhormones called estrogen and progesterone.Ovulation is the process of releasing matureovum from the ovary. Normally one ovummatures per month

 You must have now understood the structure andfunction of gametes in human beings.Compare the characteristics of sperms and ova andcomplete the given table suitably

 

If fertilization fails to occurAlong with ovulation, the preparations for the growthof foetus take place in the uterus every month.Endometrium, the inner layer of uterus thickens andmore blood capillaries and glands begin to develop.But when fertilization does not take place, all thesepreparations become futile. The newly formed tissuesget destroyed and they peel off from the uterine wall.These tissues get eliminated through the vagina alongwith blood and mucus. This process is calledmenstruation. It may last for 3 – 7 days

 Basic Science VIII202Menstruation: a naturalprocessMenstruation is a naturalbiological process that takesplace in girls as part of theirphysical growth. Menstruationstarts early or late, inaccordance with one’sheredity, food habits, state ofhealth or hormone variations.Prior to menstruation, mildback pain, pain in lowerabdomen, nausea etc., may beexperienced. The duration ofmenstrual cycle may not be thesame in every individual.Generally menstrual cyclerepeats once in 28 days. Forthe first one or two years,menstrual cycle may beirregular. If the irregularitycontinues, medical assistanceshould be sought. It is also veryimportant to maintainmenstrual hygiene. Menstrualcycle stops around 45 – 50years of age

 If fertilization occursThe ovum released from the ovary reaches the oviduct.There it fuses with the sperm and forms the zygote.This process is called fertilization. Though manysperms reach the oviduct only one sperm fuses withthe ovum. The single celled zygote undergoes divisionto become a multicellular embryo. Embryo developsby attaching itself to the endometrium, the inner layerof uterus

 HormonesHormones are chemicalsubstances produced in theendocrine glands of the body.Hormones control and co-ordinate various life processes.Therefore any variation in thesecretion of hormones affectsthe life processes considerably

 Illustrate through a flow chart the various stages from ovulation to thebeginning of embryonic development in the uterus

Basic Science VIII204Placenta is the part by which the embryo attaches itself to the endometrium anddevelops. Placenta is composed of foetal tissues and uterine tissues. Oxygen andnutrients reach the foetus through the umbilical cord developed from placenta. Wastematerials are also eliminated through the placenta. Placenta helps in the exchangeof materials between the mother and the foetus without mixing their blood. Thegrowth of the foetus completes within the amnion, the membraneous covering formedfrom the embryonic cells during the initial stages of growth. The amniotic fluid withinthis covering prevents dehydration of the foetus and protects it from shocks

 The gestation period of human beings is about 270 – 280 days.During this period , the foetus completes its growth through gradualchanges and the fully grown baby comes out through the vagina.This process is called parturition.The growth of foetus and the birth of the baby are complexprocesses. Only a woman with physical and mental maturity canaccept these changes and give birth to a healthy baby

The gestation period of human beings is about 270 – 280 days.During this period , the foetus completes its growth through gradualchanges and the fully grown baby comes out through the vagina.This process is called parturition.The growth of foetus and the birth of the baby are complexprocesses. Only a woman with physical and mental maturity canaccept these changes and give birth to a healthy baby.

 Complete the given table suitably.Observe the illustration showing the different stages of growth in human beings.ParturitionOf these, what stage do you belong to? Read the description given below andidentify the characteristics of your stage of growth.-PartFunctionEndometriumUterusPlacentaUmbilical cordAmnion

 dolescence – a special phase in lifeAdolescence is a period of biological significance. This is a period of rapidchanges from childhood to adulthood. According to the statistics of WorldHealth Organisation (WHO), the adolescence period is from 11 to 19 years.This is a period from the onset of puberty to the completion of physical growth.Puberty relates to the physical changes that occur in individuals, therebymaking them capable of reproduction. In each individual, the adolescencebegins with physical changes. Development of brain, rapid increase in heightand weight and increased efficiency of glands are the significant features ofthis period.Changes related to adolescence are more rapid in girls than in boys. Thisis because the parts of brain that control physical and mental changesdevelop rapidly in girls. Along with the rapid physical changes, intensemental and emotional changes make adolescence a significant period inone's life.Analyse on the basis of indicators the major physical changes given below.Write down your inferences in the science diary.

 Basic Science VIII206Food – Certain tips to followBreakfast is very important. Do not skip it during busyschedule.Have right quantity of food at the right time.Choose a diet that includes fruits, vegetables andpulses.Reduce the intake of fried food items.New Delhi: In India 56% of adolescent girls and 30%of adolescent boys suffer from chronic anaemia dueto the deficiency of iron. To prevent this the Ministryof Health has launched a project to supply irontablets to 13 crores of students coming under theage group of 10 – 19 years.Source: http://unicef.in/Whatwedo/33/Adolescents-NutritionWhat is the circumstance that led to the supply of iron-folic acid tablets to students?What is the role of food habits to overcome thissituation?How should the food habits be regularised so as toensure the availability of nutrients for the rapid growthof body in adolescence?Discuss.IndicatorsWhat is adolescence?How does adolescence influence the physical andmental development of an individual?Why is the rate of adolescence growth higher in girlsthan in boys?Is there any need to be anxious about the physicalchanges during adolescence? Why?Adolescence and foodProper nutrition is necessary for rapid growth. Do youfollow food habits that ensure the availability of nutrients?Read the newspaper report given below

 Anaemia-causes andremediesAnaemia is a conditioncaused either by reduction inthe number of red bloodcorpuscles in blood or by thedeficiency of haemoglobin,the pigment in red bloodcorpuscles. When anaemic,blood loses its capacity tocarry oxygen, and the personfeels weak and exhausted. Italso causes loss of memoryand concentration asanaemia affects brain’sefficiency.Deficiency of iron in the bodyis one of the causes ofanaemia. It can be remediedby including iron rich fooditems in the diet. Though irontablets may be used as animmediate solution, it isadvisable to ensure theavailability of nutrientsthrough regularisation offood habits

 Food – Certain tips to followBreakfast is very important. Do not skip it during busyschedule.Have right quantity of food at the right time.Choose a diet that includes fruits, vegetables andpulses.Reduce the intake of fried food items

 Use sugar and salt in limited quantities.Do not be habituated to bottled drinks, packet foodand fast foods.Remember that chocolate, sweets and ice creams arenot good for health.Keep in mind that excessive likes and dislikes of fooditems will adversely affect health.Develop the habit of using seasonal leafy vegetablesand fruits available in the locality.