Ch 15-17 Flashcards
(11 cards)
Q115 Differentiate between sexual and asexual reproduction in plants. [4]
Only one parent is involved in asexual reproduction while up to two parents are involved in sexual reproduction ;
Asexual reproduction does not involve fertilisation which is the fusion of nuclei of gametes while sexual reproduction involves fertilisation which is the fusion of nuclei of gametes to form a zygote ;
Asexual reproduction is a relatively quicker method as it involves development of diploid vegetative tissues into adult organism compared to sexual reproduction being a relatively slower method involving pollination and subsequent development of zygote into adult organism ;
Offsprings of asexual reproduction are genetically identical while offsprings of sexual reproduction are genetically dissimilar ;
Q116 Differentiate between mitosis and meiosis.[3]
mitosis produces genetically identical diploid daughter cells while meiosis produces genetically dissimilar haploid daughter cells ;
mitosis produces two daughter cells per parent cell while meiosis produces four daughter cells per parent cell ;
mitosis occurs for the growth of multicellular organisms, to repair worn out tissues, and for asexual reproduction. However, meiosis occurs for the formation of gametes ;
Q117 Compare the structure of an insect pollinated flower and a wind pollinated flower and explain each difference. [6]
a. Insect-pollinated flowers produce larger pollen grains that have rough surfaces with spikes or hooks while wind-pollinated flowers produce lightweight pollen grains that are smaller with smooth surfaces.;
The rough surface of the insect-pollinated flower’s pollen grains allow it to easily adhere to the insect’s hairy body. The wind-pollinated flower’s pollen grains are lighter and more streamlined to be carried across further distances by the wind current.;
b. Insect-pollinated flowers have big and bright-coloured petals while wind-pollinated flowers have small and dull or no petals present.;
The bright-colored petals attract insect pollinators, allowing them to land on the big petals, making it easier for the insects to pollinate the flower.;
c. Insect-pollinated flowers have a small stigma contained within the flower while wind-pollinated flowers have a large feathery stigma that protrudes out of the flower.;
The small stigma in the insect-pollinated flower is positioned to receive pollen grains from the insect’s abdomen more easily as the insect collects nectar from the nectaries at the base of the flower. The large stigma protruding out of the wind-pollinated flower increases surface area to volume ratio to trap pollen grains in the wind for pollination.;
d. Insect-pollinated flowers usually have a sweet-smelling scent while wind-pollinated flowers are odorless;
The scent emitted by insect-pollinated flowers attracts more insect pollinators.;
e. Insect-pollinated flowers have short filaments with anthers contained within the flower while wind-pollinated flowers have long filaments with pendulous anthers protruding out of the flower.;
The short filaments with anthers in the insect-pollinated flower are positioned to transfer pollen grains to the insect’s abdomen more easily as the insect collects nectar from nectaries at the base of the flower. The long filaments with pendulous anthers protruding out of the wind-pollinated flower are positioned so the anthers are easily agitated by wind to release pollen grains easily.;
f. Insect-pollinated flowers have nectar and nectar guides while wind-pollinated flowers do not.;
Nectar and nectar guides are present in insect-pollinated flowers to attract insect pollinators to position themselves for pollen transfer. Wind-pollinated flowers do not have nectar and nectar guides as they do not need to attract insects for pollination.;
Any 3 from a-f
Q118 Distinguish between self-pollination and cross-pollination. [3]
Distinguish between self-pollination and cross-pollination. [3]
In self-pollination, only one parent is required, whereas in cross-pollination, up to two parents are required ;
In self-pollination, pollination is not dependent on external factors, whereas in cross-pollination, pollination is dependent on external factors, such as the presence of insect pollinators, and the wind ;
In self-pollination, offspring have less genetic variation, and are hence less likely to adapt to changes in the environment, whereas in cross-pollination, offspring have more genetic variation, and are hence more able to adapt to changes in the environment ;
In self-pollination, there is a higher probability of offspring being homozygous and hence, more likely for harmful recessive alleles to be expressed, whereas in cross-pollination, there is a higher probability of offspring being heterozygous, hence less likely for harmful recessive alleles to be expressed ;
Q119 Outline the events the occur after pollination, leading to fertilisation. [4]
After pollination, the pollen grain germinates in response to the sugary fluid secreted by the mature stigma ;
A pollen tube grows outwards from the pollen grain. The tip of the pollen tube secretes enzymes that digests tissues in the stigma, style and the ovary walls to reach the ovule ;
The pollen tube enters the ovule through the micropyle ;
the tip of the pollen tube absorbs sap, swells and bursts, thereby releasing the male gamete into the ovules ;
the nuclei of the male and female gametes fuse, in a process known as fertilisation, to form a zygote ;
Q120 Sperm is produced in the testis. State the structures through which the sperm passes on its journey to fertilise the ovum. [4]
The sperm passes from the testis through the epididymis to the sperm duct;
The prostate gland secretes seminal fluid which mixes with the sperm cells to form semen;
The semen, containing sperm, is then ejaculated out of the penis through the urethra into the vagina during sexual intercourse;
sperm cells passes through the cervix into the uterus then to the oviduct where it fertilises the ovum;
Q121 Describe the hormonal control of the menstrual cycle. [6]
From days 1-5, oestrogen level and progesterone level is low, this stimulates the uterine lining to break down and menstruation to occur ;
From days 6-11, oestrogen level gradually increases while progesterone level remains low, the increasing oestrogen level stimulates repair and growth of the uterine lining ;
Days 12-16 is the fertile period. High levels of oestrogen followed by a drop in oestrogen level stimulates ovulation at day 14 ;
From days 17-28, progesterone level increases while oestrogen level decreases. Progesterone maintains the thickness of the uterine lining and stimulates the development of more blood vessels to prepare for implantation of embryo ;
If fertilisation occurs and implantation is successful, placenta forms and secretes progesterone as corpus luteum breaks down ;
If fertilisation did not occur, the breakdown of corpus luteum will cause a decrease in progesterone level which leads to the breakdown of uterine lining, starting the next menstrual cycle ;
Q122 Describe the process of fertilisation and the events that occur after fertilisation, which enable it to develop and survive in the uterus. [5]
During fertilisation, the haploid nucleus of the sperm cell fuses with the haploid nucleus of the ovum, to form a diploid zygote;
The zygote undergoes mitosis to form a ball of cells known as embryo, which is swept by the cilia lining the inner walls of the oviduct towards the uterus;
The embryo reaches the uterus and implants into the uterine lining;
Finger-like projections called embryonic villi grow from the embryo into the uterine lining to form the placenta;
The placenta allows oxygen, nutrients, and antibodies to diffuse from maternal blood into foetal blood;
as well as metabolic waste products like urea and carbon dioxide to diffuse from foetal blood into maternal blood, hence the embryo is able to survive in the uterus;
Q123 State the functions of the amniotic fluid. [4]
Amniotic fluid supports and cushions the fetus before birth, it acts as a shock absorber as water cannot be compressed, thus protecting the fetus from physical injury;
Amniotic fluid also supports the foetus, allowing it to move freely during development;
Amniotic fluid also lubricates and reduces friction in the birth canal during birth;
Amniotic fluid is mostly made of water, which has a high heat capacity. Thus, it is able to maintain the temperature of the surroundings of the foetus;
Q124 Caffeine is a drug that targets cardiac muscles. Describe how caffeine molecules, ingested by a pregnant woman, is transport to the cardiac muscles of the foetus. [6]
When ingested, the caffeine molecules are absorbed in the small intestine via diffusion from the intestinal lumen to the intestinal epithelial cells, then into the blood capillaries;
Blood carrying the caffeine molecules is transported via the hepatic portal vein to the liver, where some of the caffeine molecules are broken down;
The hepatic vein transports blood carrying the remaining caffeine molecules from the liver to the vena cava that transports blood back into the heart;
The heart pumps the blood to the lungs through the pulmonary artery while the pulmonary vein transports blood from the lungs back into the heart;
The heart pumps blood into the aorta, which branches into arteries, leading to the placenta;
The caffeine molecules in the maternal blood diffuse from the placenta into the foetal blood capillaries;
The umbilical vein transports blood back to the foetal heart;
Blood is pumped by the foetal heart into the aorta which branches into coronary arteries that transports blood to the cardiac muscles of the foetus. The coffee molecules diffuse from the capillaries into the cardiac muscles;
Q125 Discuss the methods to reduce HIV transmission. [4]
HIV can be transmitted through unprotected sexual intercourse with an infected person where there is exchange of bodily fluids like semen, vaginal secretions, and anal secretions;
Hence, it is important to use a condom during sexual intercourse to reduce the exchange of bodily fluids, or to abstain from sex which completely removes the risk of the transmission of HIV;
HIV can also be transmitted through sharing of hypodermic needles/razors with the infected person, as the virus may enter the bloodstream of the individual;
Hence, it is important to avoid sharing infected instruments that can break skin and get contaminated with blood, and also ensure that these instruments are sterilised before use;
