Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Reproduction

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
X
Illustration You have already viewed an explanation Register now and access this and thousands of further explanations for free

Want to get better grades?

Nope, I’m not ready yet

Get free, full access to:

  • Flashcards
  • Notes
  • Explanations
  • Study Planner
  • Textbook solutions
Biology

Reproduction, the production of offspring, is essential for continuing life. If organisms could not reproduce and create offspring, life would cease to exist. Organisms have various ways of reproducing, reflecting the diversity of life on this planet. Let’s look at the ways organisms can reproduce to pass on their genes.

Sexual Reproduction and Function

The function of the reproductive system is to produce gametes - eggs and sperm.

Sexual reproduction is a type of reproduction where the nuclei of male gametes (male sex cells) and the nuclei of female gametes (female sex cells) fuse to form a zygote (fertilised egg).

During sexual reproduction, genetic material from both parents comes together to produce an offspring that is genetically different from its parents.

Sexual reproduction occurs through the process of meiosis. This process produces haploid gametes (sex cells with one complete set of chromosomes). In fertilisation, gametes from the mother and father fuse to form a diploid cell (sex cells with two full sets of chromosomes, one from each parent).

By producing genetically different offspring, sexual reproduction creates genetic diversity. Genetic diversity means having a range of different characteristics and traits within a species, causing different physical features and behaviours within a species.

Sexual Reproduction in Humans

Sexual reproduction in humans (and other animals) involves the fusion of a sperm cell (male gamete) and an egg cell (female gamete) to produce a diploid zygote (fertilised egg).

The production of gametes in humans occurs through the following processes:

  • Oogenesis (production of ova, or egg cells)

  • Spermatogenesis (production of spermatozoa, or sperm cells)

In fertilisation, the nuclei of these cells fuse to form a zygote or fertilised egg. Fertilisation occurs through the following series of stages and reactions:

  1. Sperm cells bind to the outer layer of the egg cell, the zona pellucida, and digest a tunnel through it using digestive enzymes – this is the acrosome reaction.

  2. The membrane of the sperm and egg cells fuse before the sperm nucleus enters the egg cytoplasm. The cortical reaction follows, which is essentially the hardening of the zona pellucida. This reaction prevents multiple sperm cells from fertilising the same egg.

  3. When the egg and sperm nuclei fuse, a zygote is formed.

  4. The fertilised egg then divides several times to form a blastocyst and implants itself in the uterus lining.

More information on these processes can be found in our article on Human Sexual Reproduction.

Sexual Reproduction in Plants

Sexual reproduction in plants follows similar principles to sexual reproduction in humans; the nuclei of male and female gametes fuse to form a zygote. However, there are some significant differences.

Male gametes are produced in the anthers of the flower and can be found in pollen grains, while female gametes are produced in the flower’s ovaries and stored in the ovules. Ovules in plants are structures that develop into seeds when fertilised. Take a look at Fig. 2 to familiarise yourself with the structure of a flower.

Reproduction Structure of a mature flower StudySmarterFigure 2: A figure showing the structure of a flower. Mariana Ruiz, wikimedia.com

Fertilisation in plants occurs as double fertilisation. In this process:

  1. A pollen grain lands on the stigma of the carpel and forms a pollen tube which grows downwards into the ovule (found in the ovary).

  2. As the pollen tube enters the embryo sac wall in the ovule, the tip of the pollen tube bursts, resulting in one male gamete (in the pollen tube) fertilising the egg – forming a zygote.

  3. Another male gamete (also in the pollen tube) fuses with two polar nuclei (female nuclei found in the centre of the embryo sac), producing an endosperm nucleus.

  4. The endosperm nucleus divides and forms an endosperm, providing nutrients and nourishment to the growing embryo.

These two fertilisation events are known as double fertilisation.

More information on these processes can be found in our article on Sexual Reproduction in Plants.

Sexual Reproduction in Fungi

Fungi (and plants) can reproduce both sexually and asexually. In both cases, the fungi produce spores released into the environment. These spores land and grow into fungi when environmental conditions are suitable.

Sexual reproduction in fungi occurs in three stages (see figure 2): plasmogamy, karyogamy and meiosis.

1. Plasmogamy – the nuclei of two haploid cells come together. They are not yet fused, so two different nuclei are present in the same cell.

2. Karyogamy – the two nuclei finally fuse, forming a diploid zygote nucleus.

3. Meiosis – cells in the gametangia (sexual reproduction organ in fungi) return to a haploid state through meiotic division. These cells are incorporated into spores which are disseminated into the environment.

Asexual Reproduction

Asexual reproduction is a type of reproduction that does not involve the fusion of gametes.

Asexual reproduction occurs solely by mitosis, whereby a cell divides to produce genetically identical daughter cells. Many organisms use mitosis to reproduce instead of sexual reproduction through gametes.

Asexual Reproduction in Fungi

Fungi can reproduce asexually through either fragmentation, budding or the production of spores.

The production of spores is the most common form of asexual reproduction. The parent organism produces these spores through mitosis, and they are disseminated into the environment.

Another form of asexual reproduction is fragmentation, where the thallus (body of the fungus) breaks into pieces before growing again. The mycelium (made up of thread-like network of filaments, called hyphae) can also break off and grow into more mycelia. The fruiting bodies of fungi, such as mushrooms, can grow from a mycelium spore.

Budding is another method of asexual reproduction. Here a bulge forms at the edge of a cell before undergoing cytokinesis and detaching from the mother cell.

Asexual Reproduction in Plants

Plants can undergo two main types of asexual reproduction: vegetative reproduction and apomixis.

Vegetative reproduction involves the vegetative structure of the parent plant to form new, genetically identical individuals through processes such as budding. This form of reproduction does not require seeds or spores.

Apomixis is a form of asexual reproduction that produces seeds without fertilisation. The ovule gives rise to a new seed. In some plants, pollination is required to initiate embryo growth, but no genetic material is transferred from the pollen grain to the offspring.

Asexual reproduction in prokaryotes

Prokaryotes, such as bacteria, are single-celled organisms that do not contain a distinct nucleus or other membrane-bound organelles. They reproduce by asexual reproduction, which occurs through a process known as binary fission. The process of binary fission is as follows:

  1. The DNA in the prokaryotic cell replicates, doubling the number of chromosomes. Remember that, unlike in eukaryotic cells, the genetic material in prokaryotes is not contained in a nucleus. Therefore, the DNA is found loose in the cytoplasm, albeit in a specialised region called the nucleoid.

  2. The chromosomes separate to opposite ends of the cell. The cell also elongates, forming a septum in the middle.

  3. A new cell wall is formed from the septum, which splits down the middle, releasing two genetically identical prokaryotic cells.

It is, however, important to note that binary fission is not strictly restricted to prokaryotic organisms. Some single-celled eukaryotic organisms may also reproduce in this way, such as amoeba.

Advantages and Disadvantages of Sexual vs Asexual Reproduction

Each reproduction method presents several distinct advantages; however, they each have their own set of drawbacks.

Sexual reproduction

Here are some advantages and disadvantages of sexual reproduction.

Advantages

  • Increased genetic diversity and genetic variation are found in the offspring.

  • The species can adapt to new and changing environments due to their genetic diversity.

  • The species is largely protected from a disease outbreak. Due to the genetic variation of individuals in the species, disease is unlikely to affect all of the individuals.

Disadvantages

  • Searching for a mate requires time and energy.

  • If an individual is isolated from the rest of the population, that individual is unable to reproduce.

Asexual Reproduction

Here are some advantages and disadvantages of asexual reproduction.

Advantages

  • When environmental conditions are suitable, it can trigger a rapid increase in the population of the organisms.

  • There is no need for another mate, only one parent is required.

  • It is faster than sexual reproduction.

Disadvantages

  • There is no increase in genetic diversity or variation in a population.

  • The species may not be able to adapt to changing environments.

  • A disease outbreak is likely to affect all individuals.

Reproduction - Key takeaways

  • Sexual reproduction can only occur through cells created through the process of meiosis.

  • Asexual reproduction occurs through the process of mitosis.

  • Humans and other mammals reproduce sexually, and cannot reproduce asexually.

  • Plants and fungi can reproduce both sexually and asexually.

  • There are advantages and disadvantages to both types of reproduction.

Frequently Asked Questions about Reproduction

Sexual reproduction is the process where the nuclei of male gametes (male sex cells) and the nuclei of female gametes (female sex cells) fuse together to form a zygote (fertilised egg). 

Reproduction is the process of producing offspring through either sexual reproduction or asexual reproduction

Asexual reproduction occurs by mitosis

Sexual reproduction involves haploid sex cells (produced via meiosis) and fertilisation to produce a dyploid zygote, and so requires two parents, whereas asexual reproduction only requires one parent, and does not need gametes or the process of meiosis to occur. The offspring in sexual reproduction are not genetically identical, but in asexual reproduction they are genetically identical.

Advantages of asexual reproduction:

  • When environmental conditions are suitable, it can trigger a rapid increase in the population of the organisms

  • There is no need for another mate, only one parent is required

  • It is more quicker than sexual reproduction

Final Reproduction Quiz

Question

What cells are contained in the ovaries?

Show answer

Answer

Oocytes,  which mature to become egg cells or ova. 

Show question

Question

The fimbriae connect what to what? 

Show answer

Answer

Ovary to fallopian tubes

Show question

Question

What is the uterus?

Show answer

Answer

A muscular, pear-shaped organ, becomes known as the womb during pregnancy. 

Show question

Question

What is the cervix?

Show answer

Answer

The lowering end of the uterus, containing the opening to the vaginal canal. 

Show question

Question

What process creates gametes?

Show answer

Answer

Meiosis

Show question

Question

What cell is created in the testicles? 

Show answer

Answer

Sperm

Show question

Question

The vas deferens carry what to where? 

Show answer

Answer

Sperm from the epididymis to the ejaculatory ducts

Show question

Question

What process forms egg cells? 

Show answer

Answer

Spermatogenesis

Show question

Question

What process forms sperm cells

Show answer

Answer

Spermatogenesis

Show question

Question

What is the outer layer of the egg cell that sperm cells bind to called?

Show answer

Answer

Zona Pellucida

Show question

Question

The acrosome reaction does what?

Show answer

Answer

Creates a tunnel into the zona pellucida to allow sperm cells to reach the membrane, by using enzymes to digest the outer layers of the egg.  

Show question

Question

What reaction occurs after fertilisation of the egg cell?

Show answer

Answer

The cortical reaction

Show question

Question

What occurs during the cortical reaction?

Show answer

Answer

Calcium ions released by nuclear fusion stimulates the release of cortical granules into the zona pellucida. These harden the zona pellucida and remove binding proteins, preventing further sperm entry. 

Show question

Question

A fertilised egg is known as?

Show answer

Answer

A zygote

Show question

Question

The binding of the blastocyst to the uterus wall is known as?

Show answer

Answer

Implantation

Show question

More about Reproduction
60%

of the users don't pass the Reproduction quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.