Reproduction

Biology Reproduction

Organisms reproduce in all sorts of weird and wonderful ways. Scientists recently discovered that a type of ﬁsh that existed over 360 million years ago was the ﬁrst to to have sexual intercourse. That set the pattern for many animals, including humans, up to today.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmoslessons.com Introduction: Reproduction

Scientists have discovered the origins of sexual intercourse by studying fossils of armour-plated 㡙sh called antiarch placoderms. This type of 㡙sh became extinct 360 million years ago.

Antiarch placoderms – which gave rise to all current vertebrates with jaws, including humans – were the 㡙rst animals to develop speci㡙c male and female genitalia.

Before them all creatures – which almost all still lived in the oceans at this time – reproduced by means of external fertilization. That means they expelled their eggs and sperm into the water to unite – as many modern 㡙sh still do. But the scientists found evidence that the placoderms changed all this. They discovered structures in the fossils that they interpret as bony "claspers" – male organs that they believe penetrated the female to deliver sperm. The positions of the claspers mean that the placoderms would have had sex side-by-side.

But the discovery that these animals had penetrative sex is perhaps less surprising than the fact that the bony 㡙shes that evolved from them show no evidence for internal fertilization. That means that some of the placoderms' descendants had to "re-invent" sex organs such as claspers in sharks and rays, and penises in mammals and birds.

Read the full Cosmos Magazine article here.

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Credit: HD animation showing the earliest known copulation by Flinders University (YouTube).

1 Poll 1

Hypothesize: While the antiarch placoderms are the 㡙rst known organisms to have had sexual intercourse, organisms have been reproducing sexually for approximately 2 billion years. Other organisms reproduce asexually – that is, without a partner.

Without doing any research, suggest which of the following organisms you think reproduce sexually.

Note: Some organisms can reproduce both sexually and asexually!

Koalas

Bacteria

Yeast

Sea anemone

Cacti

2 Gather: Reproduction

Sexual reproduction

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Credit: Sexual Reproduction by Mark Drollinger (YouTube).

3 Question 1

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional, but we recommend taking notes – they will help you remember the main points of the video and also help if you need to come back to answer a question or review the lesson.

Sexual reproduction requires two parent cells. These are special sex cells, known as gametes, and each holds half of the genetic information of their parent. Male gametes are known as sperm and female gametes are known as eggs, or ova (singular: ovum). spring hold a full complement؀When the two gametes fuse a zygote is formed, in a process known as fertilization. The o of genetic information – half from the male and half from the female.

Question 2

Deᱜne: In your own words, dene the term sexual reproduction.

Question 3 Question 4

Recall: The male gametes are known as eggs. Recall: Female gametes contain 50% of the female's genes. True True False False I'm not sure I'm not sure

Question 5

List: In the table below, describe internal and external fertilization and provide an example of a species that uses this type of fertilization.

Type of fertilization Brief description Example

Internal fertilization

External fertilization

4 Asexual reproduction

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Credit: Asexual Reproduction by Mark Drollinger (YouTube).

Question 6

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

Question 7

Deᱜne: In your own words, dene the term asexual reproduction.

5 Question 8

Identify: The video clip describes three types of asexual reproduction: cell division, budding and splitting. Drag the labels into the boxes to indicate the method of asexual reproduction used by each type of organism.

6 Process: Reproduction

Whether sexually or asexually, organisms reproduce in all sorts of weird and wonderful ways. In the case of the redback and dark 贄shing spiders the males are eaten alive by the female during sex!

The following fun facts about the dark 贄shing spider will help you answer questions 1–4 below:

During mating season the males outnumber the females 3:1. The weight of the female spider is 14 times that of the male. Each female can produce 1000 spiderlings, which she carries around and guards in a webbed nest.

7 Question 1 Question 2

Calculate: A population of dark 贄shing spiders has 20 Calculate: At the beginning of mating season a population females. How many males spiders would you expect there of dark 贄shing spiders has 30 males. How many female to be at the beginning of mating season? spiders would you expect there to be?

Question 3 Question 4

Calculate: A female dark 贄shing spider was found to Calculate: There are 15 male dark 贄shing spiders in a weigh 7 grams. What would you expect a male to weigh? population. How many oఅspring could be produced?

8 Question 5

Investigate: Complete the table below. For the "Parental care rating" use the following system:

"0" – parents take no care of oఅspring.

"1" – parents care for seeds or fertilized eggs.

"2" – parents care for oఅspring after they are born or hatched.

For the other columns use the answers below:

Zygotes develop into seeds in fruit before dispersal by being eaten | Oఅspring spends 1 month developing in uterus then 7 months in pouch living on mother's milk and pap. Then stays another 5 months carried on mother's back | Parents not present at fertilization – no care of oఅspring. Split individuals are fully developed, just need to grow new arms.

O正spring Number genetically Parental Method of of Number of o正spring: Parental care: Organism Image identical care reproduction o正spring Notes Notes to rating per year parents?

Can’t identify parents Escherichia – 1 individual coli becomes 2 A common Yes "daughter" gut bacteria individuals, fully developed.

Phascolarctos cinereus Sexual 1 Koala (internal)

Thousands of eggs and sperm released into the ocean seasonally where Ophiactis they are fertilized. Many savignyi 0 oఅspring eaten. Brittle star Often individuals split to produce two new individuals.

Carnegiea Only starts 贄owering at gigantea 30 years old. 2,000 seeds per fruit, 20–100 fruit per Saguaro plant. Very few seeds cactus grow to maturity.

Female keeps egg sac in her web for 3–6 Latrodectus weeks until young hasselti emerge. They stay on 1,000 to Redback the web a few days, 2,500 spider sometimes eating siblings, before leaving.

9 Question 6

Think: What are some of the advantages and disadvantages of sexual and asexual reproduction? Propose why each may have led to evolutionary success.

Hint: You may share ideas about this task in the discussion board at the bottom of this page. If it is closed ask your teacher to open it.

10 Project: Reproduction

Sexual vs. asexual reproduction

Question 1

Imagine: Write a 200 to 250-word essay in response to the following question:

"If there were only asexual reproduction, how would this aect the world as we know it?"

Use the project space below to construct your essay. You may wish to use a mind map to brainstorm your ideas and the text widget to write your essay.

11 Career: Reproduction

As a child from a small village in Slovenia, Simona Kralj-Fišer didn't know she wanted to be a scientist. She didn't even know that such a profession existed. Simona thought that the only way to have a career in science was to be an astronaut, with the next best option to be a medical doctor. And so she dreamed of becoming a doctor.

When Simona had to choose the subjects she wanted to study in school she was torn between her interests in biology, psychology, geography, and literature. Finally, she settled on biology – and soon realised there was more to science than just medicine and space travel.

Now, she is a researcher and lecturer of behavioural genetics at the Slovenian Academy of Sciences and Arts, where she's a specialist in the curious mating behaviours of nephilid spiders. There's no shortage of interesting and exciting things when it comes to the spiders, like how female spiders are physically incapable of mating more than twice in their lives. But what fascinates Simona the most about the spiders is possibly the most bizarre aspect of their behaviour – female spiders eat their mates after mating. It's a thrilling thing to watch, although Simona admits she always hopes the poor male spider will survive its romantic encounter!

Like many other scientists, every day at work is dierent for Simona. She does everything from the most technical work that involves rearing her spiders and doing lab maintenance, to carrying out experiments, analysing data, writing papers, and teaching her students. But her favourite thing to do is watch her spiders at work.

When she isn’t attending to her arachnids, Simona makes time for her hobbies, which include reading, hiking, collecting mushrooms and fruit from the forest, and spending time with her family.

12 Question 1

Imagine: When she took biology at school Simona discovered that there was more to science than being a doctor or astronaut. In fact, there is a science angle to many of the activities we undertake or interests that we have in our everyday lives.

Write down two or three things that you enjoy doing, and some of the dierent ways that science is involved in these.

Image credits

Getty images, Shutterstock, iStock & Adobe Stock.

13 Test: Reproduction

Note: There may be more than one correct answer to the multiple-choice questions below.

Question 1 (1 mark) Question 2 (1 mark)

Asexual reproduction requires two individuals. Sexual reproduction produces genetically identical individuals. True True False False I'm not sure I'm not sure

Question 3 (1 mark) Question 4 (1 mark)

How are sex cells (gametes) diఅerent to normal body cells? Which cell is the female gamete?

Pick the best answer. Bacterium

They are bigger in size Sperm

They are smaller in size Ovum (egg)

They have only half the amount of genetic Zygote information

They have twice the amount of genetic I'm not sure information

They aren't diఅerent – they are the same

I'm not sure

14 Question 5 (1 mark) Question 6 (1 mark)

When sex cells fuse together, what do they form? When sex cells fuse together, what is this process called?

A zygote Reproduction

A sperm cell Fertilization

An egg cell Ovulation

A body cell Cell division

I'm not sure I'm not sure

Question 7 (1 mark) Question 8 (1 mark)

Which of the following is/are form(s) of asexual Why do oఅspring of sexually reproducing parents look reproduction? similar, yet not exactly like their parents?

External fertilization They have the same genetic information as their father Budding They have the same genetic information as Splitting their mother They have exactly the same genetic Cell division information as both of their parents

I'm not sure They have a mix of half the genetic information from each parent

I'm not sure

Question 9 (1 mark) Question 10 (1 mark)

In most spiders, the male deposits a packet of its sex cells Considering the examples from the lesson, larger, on a bit of web and then picks it up with its pedipalps (like complex, multi-cellular organisms reproduce: small arms) and puts it into the female's genital opening. The female fuses the cells with the gametes inside her asexually body at a later time, when conditions are good. sexually This is an example of: I'm not sure internal fertilization

external fertilization

budding

cell division

I'm not sure

15 Question 11 (1 mark) Question 12 (1 mark)

Clones are genetically identical copies of an organism. Some organisms can reproduce sexually and asexually. Which method(s) of reproduction produce clones? True Internal fertilization False External fertilization I'm not sure Budding

Splitting

I'm not sure

Question 13 (1 mark) Question 14 (1 mark)

Only animals, such as mammals, birds and 贄sh, reproduce A particular species breeds using internal fertilization and sexually. the young stay with the mother for over a year, requiring feeding and care. True How many young are the members of this species most False likely to have at a time?

I'm not sure 2

200

20,000

I'm not sure

Question 15 (1 mark) Question 16 (1 mark)

A type of marine animal has genetically diఅerent oఅspring In stable environmental conditions a perfectly adapted to itself and releases many thousands of eggs with very organism survives well and can use asexual reproduction few surviving to adulthood. to produce lots of oఅspring equally suited to the environment. What is the reproductive method of this animal? But if environmental conditions change, sexual Internal fertilization reproduction can be an advantage. Why?

External fertilization It will be easy to 贄nd partners for sexual reproduction Splitting Sexual reproduction is often a slower process Cell division than asexual reproduction

I'm not sure Any change in the environment will cause all asexually reproducing organisms to die out

Sexual reproduction produces genetically diఅerent oఅspring who may be better suited to the changing conditions

I'm not sure

16 Question 17 (1 mark)

Learning goal 1: Identify two diఅerences between sexual and asexual reproduction.

Question 18 (1 mark)

Learning goal 2: Brie贄y describe the three main types of asexual reproduction.

Question 19 (1 mark)

Learning goal 3: Explain one advantage of asexual reproduction and one advantage of sexual reproduction.

Total available marks: 19