Transcript reproduction - Teaching Biology Project

1. SEXUAL AND ASEXUAL
2. LIFE CYCLES OF PLANTS AND INSECTS
3. FLOWERS AS REPRODUCTIVE
STRUCTURES
4. REPRODUCTIVE STRATEGIES IN ANIMALS
COMPARING ASEXUAL AND
SEXUAL REPRODUCTION
Definition of asexual
reproduction:
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No fertilisation
Only one parent
No genetic variation
as opposed to ...
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1.
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3.
4.
Fertilization
Two parents
Genetic variation
Gametes fuse to form zygote, containing genes
from both parents.
Further variation brought about by:
Crossing over during meiosis, prophase I
Random assortment and segregation of
chromosomes
Random fertilisation
Mutations
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Types of asexual reproduction
1. Binary fission
– “splitting in two” –
mitosis, e.g. bacterium: Escherichia coli
Lorraine Kuun, July 2011
Types of asexual reproduction
2.
Budding – new individual develops as
outgrowth on parent organisms e.g. Yeast cells.
Lorraine Kuun, July 2011
Types of asexual reproduction
3. Spore production – spores produced during
favourable conditions e.g. Fungi
Lorraine Kuun, July 2011
Types of asexual reproduction
4. Vegetative reproduction
– vegetative
part of plant, i.e. root, stem of leaf develops
into new plant; can be natural or artificial.
Buds on leaf
margins e.g.
Kalanchoe
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NATURAL – Runners, Rhizomes and bulbs and tubers
Bulbs
Tubers
ARTIFICIAL: Cuttings, Grafting and tissue cultures
ADVANTAGES
OF ASEXUAL REPRODUCTION
1.
2.
3.
4.
Large number of offspring
Reproduction process is fast
Energy expenditure low – no mates needed,
no gametes produced
Offspring well-adapted to environment in
which parent lives
ONE CONDITION: environment
must be
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DISADVANTAGES OF ASEXUAL
REPRODUCTION
1.No genetic variation –
adaptation may be difficult
2.All share same “weak
characteristics” – may die out
when environmental conditions
change/become unfavourable
3.Mass reproduction can threaten
environment – carrying capacity
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ADVANTAGES OF
SEXUAL REPRODUCTION
1.Genetic variation
2.Possible better
adaptations to changing
environment
3.Role in natural selection
4.Better chances of survival
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DISADVANTAGES OF
SEXUAL REPRODUCTION
1.High energy cost – gametes to be
produced, gestation, parental care
etc.
2.Needs two parents
3.Slower, longer process
4.Young can be vulnerable to
predators
5.Extended periods of parental care
6.Plants may need pollinators
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1. Alternation of generations: haploid (n) stage
(
) that produces
followed by diploid (2n) stage
(
) producing
.
2. Haploid: gametes; half the number of
chromosomes in somatic cell, indicated by
n, result of meiosis.
3. Diploid: somatic cells; double number of
chromosomes in gametes, indicated by 2n;
result of fertilisation.
1. Gametophyte: generation producing
gametes in gametangium/ gametangia
sexual stage.
2. Sporophyte: generation producing spores
in sporangium/ sporangia – asexual stage.
NB: In higher plants the generations alternate
in the life cycle of a plant; in lower plants
reproduction is either through gametes
(sexual) or spores etc. (asexual).
1.
A haploid gametophyte generation that
produces gametes (n) by mitosis ...
the gametes (n) fuse to
form zygote (2n), the start of ...
2.
A diploid sporophyte generation that
produces spores (n) by meiosis.
Leaf-like structures of
moss gametophyte
Sporangium of
moss sporophyte
INSECT METAMORPHOSIS
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Physical changes from one stage in life cycle
to another.
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TWO TYPES OF METAMORPHOSIS:
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1. Complete metamorphosis
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2. Incomplete metamorphosis
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COMPLETE
Four stages:
1. egg
2. larva
3. pupa
4. adult
E.g. Butterflies, bees,
housefly
88 % of all insects
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INCOMPLETE
Three stages:
1. egg
2. nymph
3. adult
E.g. Locust, cricket,
cockroach
12 % of insects
Advantages:
1. Larva and adult
occupy
and niches –
not in competition.
2. Carrying capacity of
ecosystem increased.
3. Egg and pupa stages
allow insect to
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.
Disadvantages:
1. Larval forms
vulnerable to
.
2. Suitable habitat
for laying of eggs
needed.
3. Change from pupa
to adult requires
high energy-input.
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 Disadvantages:
Advantages:
1. Vulnerable pupa 1. Nymph and adult often
compete for same food.
stage avoided.
2. Insect vulnerable to
2. Less energy is
dehydration and
needed – no
predators when
drastic changes
moulting.
from pupa to
3. Entire insect population
adult.
could be threatened by
3. All stages can eat
environmental changes.
same food.
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Lorraine Kuun, July 2011
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The
are the
male organs (anther +
filaments) and produce
pollen that contain the
male gametes
The
with the
(stigma +style +
ovary) is the female
organ of the plant. The
ovums/ova are found
IN the ovule.
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1. Male (no pistil) or female (no anthers)
flowers on different plants – dioecious.
2. Protandry – pollen ripe before stigma is
receptive.
3. Protogyny – stigma receptive, but pollen
not ripe yet.
i.e. self-pollination is prevented.
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Most pollinators are
insects e.g. Bees,
moths, butterflies,
beetles.
Some vertebrates
also pollinate
flowers e.g. Bats,
mice, birds (mainly).
Many flowers are
pollinated by wind.
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Bright colours (bees cannot see red), white for
night pollinators e.g. moths
Often sweet scent (attracts moths and
butterflies)
Reward of nectar and pollen
Contrasting markings on petals to locate
centre of flower (usually not visible to human
eye – ultraviolet)
Pollen cling to hair on insect bodies
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High yield of dilute nectar
Bigger than most insect-pollinated flowers
Open in daytime, often red
Sturdy against rough feeding of birds
Little or no scent – birds have poor sense of
smell
Protect ovary against beaks by being inferior
or by partition
Pollen sticks together in clumps
Often erect or with landing platform for birds
that do not hover
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Flowers do not have scent, nectar or brightly
coloured petals – no need to attract
pollinators.
Flowers high on plant to be exposed to wind.
Flowers usually small and reduced, lacking
calyx or corolla (sepals and petals).
Anthers large and well-exposed.
Masses of light, non-sticky pollen produced.
Stigmas long and feathery with large area for
trapping pollen.
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Lorraine Kuun, July 2011
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The ovary develops into the fruit, the
ovule into the seed.
 The
fruit
develops from
the following
layers:
• Fruit wall from
ovary wall.
• Seed from ovule.
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A seed
consists of a
1. Seed coat –
outer layer of
ovule (pericarp).
2. Embryo – from
fertilisized egg
cell (zygote
undergoes
mitosis).
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Endosperm
– result of
double
fertilization.
Endosperm
is food for
embryo –
also why we
eat seeds
for food.
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Resistant to unfavourable conditions as they
have seed coat.
Can be dispersed effectively (see later).
Can remain viable in dormant state for long
periods.
Seeds have stored food reserve in endosperm
or cotyledons; includes starch, oils and or
protein.
Important to man as they are cheap form of
plant propagation, way to store plants and
are a store of food.
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Dormancy is a state of rest. Embryo inactive,
seed will not germinate.
Some plants have obligatory period of
dormancy – seed will not germinate even if
conditions are favourable.
Dormancy prevents seeds from hatching in
wrong season when seedlings would be
exposed to unfavourable conditions. Allows
seeds to survive unfavourable conditions.
Allows for seed dispersal agents to act.
Lorraine Kuun, July 2011
Agents for seed dispersal
Wind – seeds are light with plumes or
wings.
 Animals – hooks and thorns – cling to
wool, stick in paws.
 Humans – edible fruit – seeds egested
in different position.
 Water – seeds contain oil or air
bubbles – float away.
 Self-dispersed – fruit dry, dehiscent.
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Lorraine Kuun, July 2011
COCO DE MER drifts
along ocean currents
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Most important plant source of food for
humans.
Practical form of food – easy to transport and
store for long periods of time.
Grains – wheat, maize (mealies), sorghum,
rice, oats; mainly starch
Pulses (legumes) – beans, peas, soy beans,
peanuts, lentils, plant proteins
Nuts – oily seeds in hard shells e.g. walnuts,
cashews, pecans etc.
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Many plant species under threat.
Seed bank stores seeds of wild plants and crops.
UK – conserves seeds of about 10% of wild plant
species at Kew – Millennium Seed Bank Project.
Swedish International Seed Vault – reinforced
concrete tunnel – 4,5 million seed samples – will
remain viable for 1000’s of years.
MSBP working with SA National Biodiversity
Institute – contributing 2500 indigenous species
– endangered, endemic, over-exploited
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Can be used to
1. re-establish damaged, lost habitats and
ecosystems
2. re-introduce extinct, endangered or
threatened species
3. provide research material
THANK YOU
Lorraine Kuun, July 2011
THE ULTIMATE GOAL OF EACH SPECIES
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To produce the maximum number of
surviving offspring ...
while using the least amount of energy.
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This is called the
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reproductive effort.
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3.
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5.
6.
Courtship
External vs Internal fertilisation
Ovipary, ovovivipary and vivipary
Precocial and Altricial
development
Amniotic egg
Parental care
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 Simple
strategies include
pheromones (chemical),
brightly coloured body
parts (visual) and mating
calls (auditory) stimuli.
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Lorraine Kuun, July 2011
 Complex
strategies, unique
to species, include
courtship displays, annual
rut (period of sexual
excitement), lek breeding
system, courtship-feeding.
Lorraine Kuun, July 2011
Courtship display strategies unique to
each species; can include movement, calls,
seasonal colour patterns etc.
Bluecrane male trying to attract
female’s attention by an elaborate dance
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1.
2.
Females will be in peak condition
to nurture developing baby.
Young are born when enough
food is available to enable them
to reach reproductive age.
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Lorraine Kuun, July 2011
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Above: male springbok display
Left: male cichlids make bowers
for females to lay eggs
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Male hoopoe feeds female;
if she accepts, they will mate
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Males and females find suitable mates e.g.
male with best genetic potential.
Sexual behaviour in courtship is timed so that
male and female both ready for mating at
same time.
Energy expenditure by male; female
conserves energy for breeding.
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 Disadvantages
of external
fertilisation (outside the body):
1. Wasteful; huge loss of energy –
many eggs produced, few
survive.
2. Fertilisation not certain.
3. Environmental conditions
important for hatching of eggs
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Huge numbers of eggs increases probability of
fertilisation.
Courtship rituals ensure that males and females
are closer to each other.
Eggs of marine species release species-specific
chemotactic factor to attract sperm.
Spawning is timed to occur when ocean currents
can disperse eggs e.g. sessile species.
Young easily dispersed by sea currents; reduce
competition.
No complicated physical mating, using energy.
Larval form gets food directly from environment;
no energy input from parent.
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Mating occurs, but no copulation
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Occurs in insects and terrestrial vertebrates i.e.
birds, reptiles and mammals.
Marine mammals and some fish e.g. sharks and
rays also have internal fertilisation.
Mating and copulation occurs.
Most animals have cloaca – common opening for
reproduction and egestion – during fertilisation
cloacas are lined up.
Male insects and mammals have a penis – organ
to transfer sperm to body of female.
Fluid inside female provide medium for sperm to
swim towards egg cell(s).
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1.
2.
Fertilisation is more certain –
gametes placed closer together.
Fewer gametes needed.
Energy saved in producing fewer
gametes can be used for other
purposes.
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Yolk to feed young.
2. Shells that enclose eggs (oviparity); better
protection increases survival rate.
3. Some fertilised eggs very well-protected
e.g. Sharks (ovoviviparity) and mammals
(placenta).
4. Less wastage of gametes – in humans one
egg per month produced.
There is a disadvantage: a cooperative partner
is needed!
1.
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Lorraine Kuun, July 2011
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OVIPARY – eggs are released and develop outside
body of female, fertilisation internal or external,
egg yolk only nutrition.
OVOVIVIPARY – Internal fertilisation, egg shell
soft, eggs hatch inside body, appears to be born
alive, egg yolk nutrition, mother for protection.
VIVIPARY – fertilisation internal, no egg shell,
nutrition via placenta.
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 Most
fish, amphibians and lower
aquatic forms.
 Needs large numbers of eggs.
 Larval stage self-sufficient; don’t
compete with parents – use
different food sources.
 Eggs and larvae easily dispersed.
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Invertebrates produce large numbers of eggs
to ensure survival (no or little parental care).
Protective shell prevents embryo from drying
out.
Fewer eggs in e.g. birds and reptiles – energy
can be used for more food in egg (yolk and
albumin), hatching and protection, parental
care.
Development of amnion important factor in
success.
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Hard shell good protection for developing embryo;
prevents embryo from drying out.
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Shark egg pouch with yolk clearly visible
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2.
3.
4.
5.
Fewer eggs needed – higher survival rate of
offspring.
Developing embryo much less vulnerable to
predators.
Developing embryo not subject to
environmental changes e.g. temperature.
Young born fully developed, can feed and
escape predators more easily.
Occurs in some invertebrates, fish and
reptiles.
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Lorraine Kuun, July 2011
Young puff adder being “born alive”
after hatching inside mother; note position of cloaca.
Lorraine Kuun, July 2011
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Occurs in placental mammals, some sharks
and scorpions
Fertilisation internal, no shell
Placenta responsible for nutrition – young
born alive
1. fewer eggs necessary
2. energy available for nourishment and
protection of embryo, as well as parental care
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Lorraine Kuun, July 2011
PRECOCIAL
ALTRICIAL
1. Young hatch or born 1. Born or hatched
when almost fully
when not welldeveloped
developed
2. Open eyes, hair or
2. Often naked, lacking
down
hair or down
3. Active or mobile
3. Cannot walk or fly
4. Not confined to
4. Confined to nest or
nests
burrow
5. Energy goes into
5. Energy goes into
prenatal
parental care after
development
birth
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Ground-nesting birds e.g. Penguins,
domestic poultry, ostriches
Large mammals e.g. Elephants, species of
antelope, horses etc
Allows young to fend for itself, feed and stay
warm
Stay with herd for protection against
predators
Learn from older individuals in herds
OFFSPRING HAS GOOD CHANCE OF SURVIVAL
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Left: Penguin chick and
Above: foal, both mobile
soon after birth
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Small animals that produce big litters e.g.
mice, rats, cats, dogs
Tree-nesting birds that have nests away from
predation
Humans (see human reproduction)
Altricial species need parental care for a long
time – usually female that does the caring,
male sometimes involved.
Birds usually have mouth-lining or gapeedge
Mammals small and immature brains
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Altricial bird – see mouth-lining that attracts mother
Lorraine Kuun, July 2011
Mice survive in broods,
cared for by mother (left);
Kittens born weak and totally
dependent on mother (below)
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Adaptation of later vertebrates; can lay eggs
in terrestrial environment.
Amniotic egg has fluid-filled, extraembryonic membranes that prevents embryo
from drying out.
Earlier vertebrates lay eggs in water; need to
return to water/live in water to reproduce.
Amniotic egg lessens dependence on water
for reproduction.
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Fertilisation is internal.
 Extra-embryonic (not part of embryo)
membranes only develop after fertilisation.
 Membranes are:
1. Amnion
2. Allantois
3. Yolk sac
4. Chorion
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Major evolutionary development; allowed first
reptiles to colonise land!
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Lorraine Kuun, July 2011
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The fluid-filled amnion surrounds and protects
the embryo, especially against dehydration and
shock.
Allantois acts as reservoir for nitrogenous waste
in birds and reptiles.
Yolk sac holds nutritious food for development of
embryo.
Chorion surrounds all other membranes: in birds
it allows for gaseous exchange; in mammals it
forms the placenta (taking over functions of
allantois and yolk sac, amongst others (see
human reproduction).
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Lorraine Kuun, July 2011
Any pattern of behaviour in which parent
spends time or energy to improve the
1survival, 2condition and 3future reproductive
success of offspring.
 Care can be given at any stage:
1. Prenatal – guarding eggs, building nests,
carrying broods, incubating eggs and
placental nourishing.
2. Post-natal – providing food, protecting
offspring, teaching offspring.
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Little or no parental care means a low
reproductive effort.
Reproductive energy put into producing
masses of eggs.
High mortality rate amongst eggs as well as
young.
Few individuals survive to reproductive age.
E.g. Most fish, amphibians, insects, most
reptiles
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Few eggs or young produced.
Low mortality rate amongst eggs or young.
High reproductive effort.
Reproductive energy goes into parental care
after birth (post-natal).
Most offspring survive to reproductive age.
E.g. Mammals, birds, some reptiles,
exceptions amongst fish and Arthropods.
Lorraine Kuun, July 2011
Right: chicken
laying egg,
mother feeding
young
Left: Midwife toad
Ovovivipary type
of parental care
Left: Male seahorse with
young emerging
from breeding pouch
Lorraine Kuun, July 2011
Lorraine Kuun, July 2011