Module 1 Flashcards
What is sexual reproduction?
Involves the meeting of gametes which carry genetic information from both parents to the offspring.
Advantages and disadvantages of sexual reproduction:
+) some offspring may possess random variations that make them better suited to new and changing environmental conditions. They may out-compete other individuals in the population, thus gaining a selective advantage. This survival gives the overall population a better chance of survival.
-) process demands a greater expenditure of time and energy, involving processes such as finding a mate, courtship behaviour, game production and mating. These processes may also make organisms vulnerable to predators.
Define asexual reproduction:
Involves only one parent and gives rise to genetically identical offspring
Advantages and disadvantages of asexual reproduction:
+) fast, good in stable, unchanging environments
-) bad for changing environment/disease due to no genetic variation
What is external fertilisation?
Involves the fusion of a sperm and ovum outside the female body.
- better suited to organisms that produce in aquatic or very moist environments
- less time and energy are required of the parents, but a large number of gametes must be produced to ensure that some young survive
Advantage of external fertilisation:
Wide dispersal of young; some marine animals release their gametes into the sea, and the fertilised eggs are carried far away from their parents to reduce competition for food, living space, and allows rapid recovery of populations in damaged areas.
Examples of external fertilisation:
- Bony fish: produce ova in large batches and release them into the water where they fuse with the sperm outside the female body. Although thousands of eggs are fertilised, many succumb to microbial infection or predators
- Amphibians: in frog and toad copulation, the male grasps the female and straddles her back, discharging fluid containing sperm onto the eggs as they are released by the female into the water.
- Staghorn coral
What is internal fertilisation?
Involves the fusion of gametes inside the female body.
- protects gametes from dehydration and loss to external elements, and protects fertilised eggs and developed young from immediate predation, therefore fewer eggs are required for the survival of a sufficient number of offspring
Examples of internal fertilisation:
- Reptiles: most reptile eggs are fertilised internally and then deposited outside the mother’s body for development
- Birds: male and female birds rub the openings of their cloacas together and sperm are transferred to the females body
- Mammals:
Monotremes (e.g. platypus): after internal fertilisation, they lay eggs that develop outside the mother’s body
Marsupials: develop internally for a short time after fertilisation and then continue their embryonic development in a pouch
Eutherians (placental mammals): following internal fertilisation, the young completes its embryonic development inside the body of the mother in the uterus, which nurtures and protects the embryo.
Similarities of internal and external fertilisation:
Sim: male and female gametes are required, zygote requires a watery environment for development, if male and female gametes are in close proximity to each other, fertilisation will occur.
Differences of internal and external fertilisation:
Gametes: In Ex large number of male and female gametes are produced, where In has large number of male gametes but fewer female gametes produced.
Conception mechanism: in EX there is a simultaneous release of gametes, in IN the male inserts sperm into the female’s reproductive tract
Chance of fertilisation: in EX it is low as male gametes are released into a large open area less successful with uniting with female gametes, in IN it is high a male gametes are released into a confined space with more change in successfully uniting with female gametes.
Environment for zygote: in EX usually external, watery environment, vulnerable to temp, predation and infection. in IN usually internal, protected environment inside female’s body with less chance of predation, infection.
How does fertilisation occur in a sexually reproductive plant?
The male gametes inside the pollen must be carried from the anthers to the stigma, process called pollination. Once pollen has been deposited on the stigma, a pollen tube germinates and grows down the style to an ovule contained in the ovary. In flowering plants, fertilisation occurs internally inside the ovary.
Differentiate between self-pollination and cross-pollination:
Self pollination in plants requires less energy as there is no requirement for the plant to produce structures to attract pollinators. The plants can grow in areas where insects/animals that visit plants are absent/few.
Cross pollination relies on outside agents to transfer pollen from anthers to stigmas; this may be abiotic agents (wind, water) or biotic agents (insects, animals). Cross pollination ensures greater variation in the offspring.
Features of pollination by wind:
- anthers are long and produce large amounts of light pollen, easily picked up by the wind
- stigma are very large and spread out in a feathery manner to trap pollen carried by wind
- wind pollination is inefficient, so large quantities of pollen are produced
Pollination by animals:
During the search of animals finding nectar, pollen rubs onto their bodies and then transferred to the next flower they visit. Flower scent, colour, shape and nectar are important in attracting animals.
What is seed dispersal?
After pollination and fertilisation of the flowers of a plant, seeds from inside the ovary are dispersed.
+) seeds are dispersed over a wide distance, this helps prevent overcrowding and competition for light, water and soil nutrients. Widespread distribution also increases chances of continuity of the species in other locations in case there is a sudden change in the local environment.
What is asexual reproduction? Advantages + disadvantages:
Does not involve production or fusion of gametes, offspring is genetically identical to the parent, no mixing of genetic information to introduce variation. This is the main form of reproduction in unicellular organisms.
+) enables organisms to reproduce quickly without having to find a mating partner as it can be complicated if they are immobile. Also comp. advantage if they live in an environment which they are well adapted to.
-) little or no variation in a population makes the whole group vulnerable to sudden changes in the environment, affecting survival.
What is vegetative propagation?
- 1 parent, mitosis, no genetic variation
New individuals arise from portions of the roots/stems/leaves/buds of adult individuals and are genetically identical to their parent - used in agriculture to increase the production of crops when seeds are difficult to germinate
Examples of vegetative propagation:
- runners: long thin modifies stems that grow along the surface of the soil (lateral shoot)
- rhizomes: underground horizontal modified stems
- suckers: lateral root, the root produces modified roots which gives rise to new plants and can spread quickly into a vacant patch of habitat after disturbance
- tubers: fast, good at colonising new land, stable environment, however bad bc there is comp with parent plant, no variation
What is budding?
An adult organism gives rise to a small bud which separates from the parent and grows into a new individual.
- when environmental conditions are favourable, a small outgrowth develops of the parent cell. As this outgrowth enlarges, the parent cell replicates its DNA, the nucleus divides and one copy moves into the bud/daughter cell. When the daughter cell reaches a certain size, it detaches from the parent cell and continues to grow until it buds in turn.
+) if there is no variation in the environment, the identical offspring will always be adapted to their surroundings
-) if the environment changes, the entire species may rapidly decline and die out
What is binary fission?
Main method of asexual reproduction in unicellular organisms such as bacteria and protists. A newly divided cell grows to twice its size, replicates its DNA, and then splits into 2 cells with identical genetic material.
- in prokaryotes (bacteria) there is no mitosis because there is no nucleus
in unicellular organisms (protists) it will involve mitosis
What is asexual reproduction in bacteria? (binary fission in specific detail)
A cell grows to twice its size, DNA replicates and separates, protein accumulates at the cleavage site, the cytoplasm divides and a new wall is synthesises.
How is binary fission and budding similar?
Both involve one parent, so no mate is required, allowing rapid proliferation of genetically identical organisms that are well suited to survive in their particular environment.
Features of spores:
- tiny unicellular reproductive cells produced in great numbers
- sporangia produces large number of spores which are light and easily dispersed, travelling long distances by wind. Spores effectively expand the distribution of the species and are able to colonise new environments.
How does mammals have sexual reproductive mechanisms to maximise reproductive success?
- internal fertilisation increases the likelihood that gametes will meet
- implantation of the embryo into the uterine wall with internal development of the embryo increases the embryo’s chance of survival
- pregnancy allows the developing young to be protected from the external environment, having constant supply to nutrients.
What are hormones?
Chemical substances (protein) that act as messengers in the body, coordinating body functions so that actions are synchronised, which is secreted by the pituitary gland.
