10

Question 1

Hypotheses explaining the advantages of producing genetically distinct offspring in spite of the costs of sexual reproduction:

Answer 1

Allows species to adapt faster than asexually reproducing ones because rare beneficial mutations that arise in different organisms can be brought together, increasing the overall fitness of the population
Allows a population to purge itself of harmful mutations more quickly
Mechanism of parasite defence: In host-parasite interactions, the host evolves defences against the parasite, and the parasite evolves new ways to infect the host, so each evolves rapidly to maintain ecological position; this requires a lot of genetic variation which is supplied more by sexual reproduction than asexual

Question 2

r-strategists

Answer 2

organisms that produce large numbers of offspring without a lot of parental investment
Evolve in unstable, changing and unpredictable environments
Advantage to reproducing quickly and producing many offspring when conditions are favourable

Question 3

K-strategists

Answer 3

organisms that produce few offspring but put in a lot of parental investment
Evolve in stable, unchanging and predictable environments, where there tends to be more crowding and larger populations
Intense competition for limited resources, so traits like increased parental care and few offspring is favoured

Question 4

yolk

Answer 4

contained in the eggs of animals that are externally fertilised; provides nutrients to developing embryo until it hatches; water and oxygen obtained directly from aquatic environment and metabolic wastes easily diffuse out

Question 5

amnion

Answer 5

membrane surrounding a fluid-filled cavity that allows the embryo to develop in a watery environment

Question 6

allantois

Answer 6

second membrane that encloses a space where metabolic wastes collect

Question 7

chorion

Answer 7

third membrane that surrounds the entire embryo along with its yolk and allantoic sac

Question 8

extraembryonic membranes

Answer 8

collective term for yolk sac, amnion, allantois and chorion

Question 9

oviparous

Answer 9

animals that lay eggs

Question 10

ovoviparous

Answer 10

embryo develop inside eggs that are inside mother until they hatch and receive nutrition from yolk not mother; mother still gives birth to live young

Question 11

viviparous

Answer 11

embryo develops inside mother and receive nutrients from mother

Question 12

molting

Answer 12

insects periodically shed their rigid exoskeleton to be replaced by a new larger one to enable growth

Question 13

follicular phase (menstrual cycle)

Answer 13

an oocyte develops and is released from ovary
Oocyte is located in a supporting shell of cells called a follicle
At the start of each menstrual cycle, FSH stimulate specific follicle cells called granulose cells to secrete a form of oestrogen called estradiol
In response to estradiol, oocytes in several follicles begin to mature each month, but usually only one becomes fully mature and the others die off
Estradiol also acts on the lining of the uterus and causes it to thicken
Estradiol acts on hypothalamus and anterior pituitary gland, where it reduces the secretion of GnRH, FSH and LH by negative feedback
At the end of the phase, the negative feedback of estradiol changes to positive feedback
Positive feedback of estradiol on the hypothalamus and anterior pituitary causes a rapid increase followed by a sharp decrease in the level of LH produced by the anterior pituitary gland
This LH surge causes ovulation, the release of the oocyte from the follicle in the ovary

Question 14

luteal phase (menstrual cycle)

Answer 14

ovulation marks the end of the follicular phase and beginning of the luteal phase
The follicle, now devoid of the oocyte, is converted to a structure known as the corpus luteum (temporary endocrine structure that secretes progesterone, which maintains the thickened and vascularised uterine lining, and estradiol, which inhibits the secretion of GnRH, FSH and LH)
Ooctye is swept into the fallopian tube and travels to the uterus
If it is fertilised, the developing embryo implants into the uterine lining
In this case, the corpus luteum continues to secrete progesterone and is first maintained by LH and then hCG which is released by the developing embryo
Eventually the placenta takes over oestrogen and progesterone production to maintain the uterine lining and stimulate forth of the uterus
High levels of oestrogen and progesterone during pregnancy also block ovulation because they suppress the release of GnRH, FSH and LH
If oocyte not fertilised, corpus luteum degenerates, estrogen and progesterone levels frops, and uterine lining is shed (menstruation)

Question 15

first trimester

Answer 15

cleavage
gastrulation
organogenesis

Question 16

cleavage

Answer 16

single large egg cell divides into many smaller cells
Molecules in egg cytoplasm (mRNA and proteins encoded by maternal genes) direct these divisions
Slower in mammals
Early division does not occur at same time in mammals
Zygotic transcription begins very early (at two-cell stage)
Pattern of cleavage different for different organisms
Morula: solid ball of cells that is product of cleavage
Further cell divisions result in a fluid-filled ball of cells called blastula/blastocyst
Implantation into uterus marks beginning of pregnancy and lasts approximately 38 weeks from fertilisation

Question 17

gastrulation

Answer 17

Gastrulation: set of cell moments that leads to reorganisation of the embryo
In humans, cells of the epiblast divide and migrate inward to form three germ layers: outer ectoderm, intermediate mesoderm and inner endoderm

Question 18

blastocyst

Answer 18

Blastocyst has an inner cell mass and outer cell layer
Inner cell mass becomes embryo and outer forms part of placenta
Inner cell mass differentiates into a bilaminar structure consisting of the epiblast and hypoblast

Question 19

organogenesis

Answer 19

transformation of the 3 germ layers into all the organ systems of the body
Ectoderm: outer layer of the skin and nervous system
Mesoderm: circulatory system, muscle and bone
Endoderm: lining of the digestive tract and lungs
Developing fetes particularly vulnerable to toxins, drugs and infections
Sex determination occurs
Y chromosome contains gene SRY which erodes protein TDF
TDF acts on developing gonad to differentiate into testis
In its absence, it develops into ovary