Parental Investment

Question 1

Features of a sperm cell

Answer 1

• very small
• copious amounts
• constant production
• food store not present
• has many mitochondria and a tail

Question 2

Features of an egg cell

Answer 2

• very large
• few produced
• produced monthly
• food store present as it nourishes the developing embryo
• has a large cytoplasm

Question 3

Which sex invests more in gamete production?

Answer 3

Females - egg cell

Question 4

How does the investment in egg cells differ between mammalian and non-mammalian species?

Answer 4

Non-mammalian females must invest in producing an egg structure that can cope with the pressures of developing outside of the body whereas mammalian females must invest in their uterus and gestation.

Question 5

What is meant by oviparous?

Answer 5

Oviparity - egg bearing (frogs etc)

Question 6

What is meant by viviparous

Answer 6

Viviparity - live bearing (humans etc)

Question 7

Benefits of oviparity

Answer 7

• reduced energy in care of young
• yolk provides good nutrient source

Question 8

Drawbacks of oviparity

Answer 8

• eggs may need to be incubated
• less chance of survival to birth (predation etc)

Question 9

Benefits of viviparity

Answer 9

• more likely that offspring survive to birth

Question 10

Drawbacks of viviparity

Answer 10

• high energy cost in terms of female carrying offspring

Question 11

Explain why the differences found between male and female gametes matter so much.

Answer 11

They mean that there is a greater investment in gametes by female than males. This has a profound influence on reproductive behaviour.

Question 12

Summarise the differences in mating behaviour between males and females.

Answer 12

• females are choosier, aiming to obtain high quality sperm to give their offspring the best possible chance of survival (and thus passing on their genes to future generations).
• males are less choosy but must compete for access to females

Question 13

Why are females choosier than males?

Answer 13

In most animals and almost all mammals, females provide for more parental investment than just the egg (prolonged gestation, placentation, lactation). A choosy female with an “expensive” gamete, arguably has more to lose than a male with regards to the success of the offspring.

Question 14

Costs and benefits of external fertilisation

Answer 14

Benefits: very large number of offspring can be produced

Costs: no (or limited) parental care means that many gametes will be predated or not fertilised and so few offspring will survive

Question 15

Costs and benefits of internal fertilisation

Answer 15

Benefits: there is an increased chance of successful fertilisation and offspring survival, which means that fewer eggs are required. Additionally the offspring can be retained internally for development/protection.

Costs: energy must be expended in order to locate a mate and gametes must then be transferred directly from one partner to another.

Question 16

R-selected species

Answer 16

• smaller
• short generation time
• reproduce earlier in lifetime
• large number of smaller offspring
• limited parental care/energy input
• most offspring do not make adulthood

Question 17

K-selected species

Answer 17

• larger and longer living
• mature more slowly
• can reproduce several times in their lifetime
• produce fewer, but larger offspring
• high level of parental care/energy input
• offspring have a greater probability of reaching adulthood

Question 18

Where are r selected species more likely to be found?

Answer 18

Tends to occur in unstable environments where the species has not reached its reproductive capacity.

Question 19

Where are k selected species most likely to be found

Answer 19

In stable environments