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

Mitochondria and Chloroplasts

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Mitochondria and Chloroplasts

All organisms need energy to perform vital processes and stay alive. That is why we need to eat, and organisms like plants gather energy from the sun to produce their food. How does the energy contained in the food we eat or in the sun get to every cell in an organism’s body? Fortunately, organelles called mitochondria and chloroplast do this job. Hence, they are considered the “powerhouses” of the cell. These organelles differ from other cell organelles in many ways, such as having their own DNA and ribosomes, suggesting a remarkably distinct origin.

Mitochondria and Chloroplasts' Function

Cells get energy from their environment, usually in the form of chemical energy from food molecules (like glucose) or solar energy. They then need to convert this energy into useful forms for everyday tasks. Mitochondria and chloroplasts are the organelles that transform the energy for cellular use, although they do this in different ways, as we will discuss.

Mitochondria

Most eukaryotic cells (protist, plant, animal, and fungi cells) have hundreds of mitochondria (singular mitochondrion) dispersed in the cytosol. They can be elliptical or oval-shaped and have two bilayered membranes with an intermembrane space between them (Figure 1). The outer membrane surrounds the whole organelle and separates it from the cytoplasm. The inner membrane has numerous inward folds extending into the interior of the mitochondrion. The folds are called cristae and surround the interior space called the matrix. The matrix contains the mitochondrion’s own DNA and ribosomes.

A mitochondrion is a double membrane-bounded organelle that performs cellular respiration (uses oxygen to break down organic molecules and synthesize ATP) in eukaryotic cells.

Mitochondria and chloroplast Diagram and microscope image StudySmarter

Figure 1. Left: diagram of a mitochondrion and its components. Source: modified from Margaret Hagen, Public domain, www.flickr.com. Right: microscope image of mitochondria inside a mammalian lung cell. Source: Louisa Howard, Public domain, via Wikimedia Commons.

Mitochondria transfer energy from glucose or lipids into ATP (adenosine triphosphate, the main short-term energetic molecule of cells) through cellular respiration. Different chemical reactions of cellular respiration occur in the matrix and in the cristae. For cellular respiration (in a simplified description), mitochondria use glucose molecules and oxygen to produce ATP and, as by-products, carbon dioxide and water. Carbon dioxide is a waste product in eukaryotes; that is why we exhale it through breathing.

The number of mitochondria a cell has depends on the cell’s function and the energy it requires. As expected, cells from tissues that have a high energy demand (like muscles or cardiac tissue that contracts a lot) have abundant (thousands) mitochondria.

Chloroplasts

Chloroplasts are found in the cells of plants and algae (photosynthetic protists) only. They perform photosynthesis, transferring energy from the sunlight into ATP, which is used to synthesize glucose. Chloroplasts belong to a group of organelles known as plastids that produce and store material in plants and algae.

Chloroplasts are lens-shaped and, like mitochondria, they have a double membrane and an intermembrane space (Figure 2). The inner membrane encloses the thylakoid membrane that forms numerous piles of interconnected fluid-filled membranous discs called thylakoids. Each pile of thylakoids is a granum (plural grana), and they are surrounded by a fluid called the stroma. The stroma contains the chloroplast’s own DNA and ribosomes.

Mitochondria and chloroplast Chloroplast diagram and microscope image StudySmarterFigure 2. Left: diagram of a chloroplast and its components (DNA and ribosomes not shown). Source: Margaret Hagen, Public domain, www.flickr.com. Right: microscope image of plant cells containing numerous oval-shaped chloroplasts. Source: HermannSchachner, CC0, via Wikimedia Commons.

Thylakoids contain several pigments (molecules that absorb visible light at specific waves) incorporated into their membrane. Chlorophyll is more abundant and the main pigment that captures the energy from sunlight. In photosynthesis, chloroplasts transfer energy from the sun into ATP which is used, along with carbon dioxide and water, to produce carbohydrates (mainly glucose), oxygen, and water (simplified description). ATP molecules are too unstable and must be used in the moment. Macromolecules are the best way to store and transport this energy to the rest of the plant.

Chloroplast is a double-membrane organelle found in plants and algae that capture energy from sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water (photosynthesis).

Chlorophyll is a green pigment that absorbs solar energy and is located in membranes within the chloroplasts of plants and algae.

Photosynthesis is the conversion of light energy to chemical energy that is stored in carbohydrates or other organic compounds.

In plants, chloroplasts are widely distributed but are more common and abundant in leaves and other green organs’ cells (like stems) where photosynthesis primarily occurs (chlorophyll is green, giving these organs their characteristic color). Organs that do not receive sunlight, like roots, do not have chloroplasts. Some cyanobacteria bacteria also perform photosynthesis, but they do not have chloroplasts. Their inner membrane (they are double-membrane bacteria) contains the chlorophyll molecules.

Similarities Between Chloroplasts and Mitochondria

As both organelles transform energy from one form to another, they have similarities related to this function. Other similarities are more related to the origin of these organelles (like having a double membrane and their own DNA and ribosomes, which we will discuss shortly). Some similarities between these organelles are:

  • An increase in the surface area through folds (cristae in mitochondrial inner membrane) or interconnected sacs (thylakoid membrane in chloroplasts), optimizing the use of the interior space.
  • Compartmentalization: The folds and sacs from the membrane also provide compartments inside the organelle. This allows separated environments for the execution of the different reactions needed for cellular respiration and photosynthesis. This is comparable to the compartmentalization given by membranes in eukaryotic cells.
  • ATP synthesis: Both organelles synthesize ATP through chemiosmosis. As part of cellular respiration and photosynthesis, protons are transported across the membranes of chloroplasts and mitochondria. In brief, this transportation releases energy that drives the synthesis of ATP.
  • Double membrane: They have the outer delimiting membrane and the inner membrane.
  • DNA and ribosomes: They have a short DNA chain that codifies for a small number of proteins that their own ribosomes synthesize. However, most proteins for mitochondria and chloroplasts membranes are directed by the cell nucleus and synthesized by free ribosomes in the cytoplasm.
  • Reproduction: They reproduce by themselves, independently of the cell cycle.

Differences Between Mitochondria and Chloroplasts

The ultimate purpose of both organelles is to provide cells with the required energy to function. However, they do so in different ways. The differences between these two organelles are:

  • The inner membrane in mitochondria folds inwards to the interior, while the inner membrane in chloroplasts does not. A different membrane forms the thylakoids in the interior of chloroplasts.
  • Mitochondria break down carbohydrates (or lipids) to produce ATP through cellular respiration. Chloroplasts produce ATP from solar energy and store it in carbohydrates through photosynthesis.
  • Mitochondria are present in most eukaryotic cells (from animals, plants, fungi, and protists), while only plants and algae have chloroplasts. This important difference explains the distinctive metabolic reactions each organelle performs. Photosynthetic organisms are autotrophs, meaning that they produce their food. That is why they have chloroplasts. On the other hand, heterotrophic organisms (like us) get their food by eating other organisms or absorbing food particles. But once they get their food, all organisms need mitochondria to break down these macromolecules for producing the ATP that their cells use.

Venn Diagram of Chloroplasts and Mitochondria

This diagram (Figure 3) summarizes the similarities and differences between mitochondria and chloroplasts:

Mitochondria and chloroplast Venn diagram comparison StudySmarter

Figure 3. Venn diagram summarizing the similarities and differences between a mitochondrion and a chloroplast. Liza, StudySmarter Originals.

Origin of Mitochondria and Chloroplasts

As discussed above, mitochondria and chloroplasts have striking differences compared to other cell organelles. How can they have their own DNA and ribosomes? The most accepted hypothesis suggests that eukaryotes originated from an ancestral archaea organism (or an organism closely related to archaea). Evidence suggests that this archaea organism engulfed an ancestral bacterium that was not digested and eventually evolved into the organelle mitochondrion. This process is known as endosymbiosis.

Two separate species with a close association and typically exhibit specific adaptation to each other live in symbiosis (the relationship can be beneficial, neutral, or disadvantageous for one or both species). When one of the organisms lives inside the other, it is called endosymbiosis (endo = within). Endosymbiosis is common in nature, like photosynthetic dinoflagellates (protists) that live inside coral cells—the dinoflagellates exchange products of photosynthesis for inorganic molecules with the coral host. However, mitochondria and chloroplasts would represent an extreme case of endosymbiosis, where most of the endosymbiont genes have been transferred to the host cell nucleus, and neither symbiont can survive without the other anymore.

In photosynthetic eukaryotes, a second event of endosymbiosis is thought to have happened. In this way, a lineage of the heterotrophic eukaryotes containing the mitochondrial precursor acquired an additional endosymbiont (probably a cyanobacterium, which is photosynthetic).

Plenty of morphological, physiological, and molecular evidence supports this hypothesis. When we compare these organelles with bacteria, we find many similarities: a single circular DNA molecule, not associated with histones (proteins); the inner membrane with enzymes and transport system is homologous (similarity due to a shared origin) with the plasma membrane of bacteria; their reproduction is similar to the binary fission of bacteria, and they have similar sizes.

Mitochondria and Chloroplast - Key Takeaways

  • Mitochondria and chloroplasts are organelles that transform energy from macromolecules (like glucose) or the sun, respectively, for cell use.
  • Mitochondria transfer energy from the breakdown of glucose or lipids into ATP (adenosine triphosphate) through cellular respiration.
  • Chloroplasts (a type of plastids) perform photosynthesis, transferring energy from the sunlight into ATP, which is used, along with carbon dioxide and water, to synthesize glucose.
  • Common features between chloroplasts and mitochondria are: a double membrane, compartmentalized interior, they have their own DNA and ribosomes, they reproduce independently of the cell cycle, and they synthesize ATP.
  • Differences between chloroplasts and mitochondria are: the inner membrane in mitochondria have folds called cristae, the inner membrane in chloroplasts encloses another membrane that forms thylakoids; mitochondria perform cellular respiration while chloroplasts perform photosynthesis; mitochondria are present in most eukaryotic cells (from animals, plants, fungi, and protists), while only plants and algae have chloroplasts.
  • Plants produce their food through photosynthesis; however, they need mitochondria to break down these macromolecules to obtain energy when a cell requires it.
  • Mitochondria and chloroplasts most likely evolved from ancestral bacteria that fused with the ancestors of eukaryotic cells (in two consecutive events) through endosymbiosis.

Frequently Asked Questions about Mitochondria and Chloroplasts

The function of mitochondria and chloroplasts is to transform the energy from macromolecules (like glucose), or from the sun, respectively, to a useful form for the cell.

Common features that chloroplasts and mitochondria have: a double membrane, their interior is compartmentalized, they have their own DNA and ribosomes, they reproduce independently of the cell cycle, they synthesize ATP.

The inner membrane in mitochondria have folds called cristae, the inner membrane in chloroplasts encloses another membrane that forms thylakoids; mitochondria perform cellular respiration while chloroplasts perform photosynthesis; mitochondria are present in most eukaryotic cells (from animals, plants, fungi, and protists), while only plants and algae have chloroplasts.

Plants need mitochondria to break down the macromolecules (mostly carbohydrates) produced by photosynthesis that contains the energy that their cells use.

Mitochondria and chloroplasts have their own DNA and ribosomes because they probably evolved from ancestral bacteria that were engulfed by the ancestor of eukaryote organisms. This process is known as endosymbiosis. 

Final Mitochondria and Chloroplasts Quiz

Question

Mitochondria are present in:

Show answer

Answer

all eukaryotic cells

Show question

Question

Where can we find chlorophyll in a chloroplast?

Show answer

Answer

thylakoids membrane 

Show question

Question

Photoautotrophic organisms obtain energy from ______ while heterotrophic organisms obtain it from _____. 

Show answer

Answer

light; other organisms

Show question

Question

Which of these organelles evolved through endosymbiosis?

Show answer

Answer

mitochondrion

Show question

Question

Where do most membrane proteins for chloroplasts and mitochondria come from?

Show answer

Answer

free ribosomes (cytoplasm)

Show question

Question

Which process is performed by mitochondria?

Show answer

Answer

cellular respiration

Show question

Question

Grana are found in:

Show answer

Answer

chloroplasts

Show question

Question

Which of these is not found in mitochondria?

Show answer

Answer

stroma

Show question

Question

The process of transferring energy from glucose or lipids into ATP (adenosine triphosphate) is called______ and is performed by______.

Show answer

Answer

cellular respiration, mitochondria

Show question

Question

The process of transferring energy from the sunlight into ATP and then using it to synthesize glucose is called______ and is performed by______.

Show answer

Answer

photosynthesis, chloroplasts

Show question

Question

Describe the similarities that mitochondria and chloroplasts have with bacteria:

Show answer

Answer

They have a single circular DNA molecule, not associated with histones (proteins); the inner membrane with enzymes and transport system is homologous (similarity due to a shared origin) with the plasma membrane of bacteria; their reproduction is similar to the binary fission of bacteria, and they have similar sizes.

Show question

Question

Where would you look for DNA molecules in a plant cell?

Show answer

Answer

nucleus

Show question

Question

Where would you look for DNA molecules in an animal cell?

Show answer

Answer

nucleus

Show question

Question

Describe 2 similarities between mitochondria and chloroplasts (consider one structural and one functional similarity):

Show answer

Answer

Structurally: a double membrane, their interior is compartmentalized, they have their own DNA and ribosomes.

Functionally: they reproduce independently of the cell cycle, they transform energy from one form to another, the synthesize ATP.

Show question

Question

Describe 2 differences between mitochondria and chloroplasts:

Show answer

Answer

Mitochondria: their inner membrane has folds called cristae, they perform cellular respiration, and are present in most eukaryotic cells (from animals, plants, fungi, and protists).

Chloroplasts: their inner membrane encloses another membrane that forms thylakoids, they perform photosynthesis, and are present only in plants and algae.

Show question

More about Mitochondria and Chloroplasts
60%

of the users don't pass the Mitochondria and Chloroplasts 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.