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4.3E: Comparing Plant and Animal Cells - Biology

4.3E: Comparing Plant and Animal Cells - Biology


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Although they are both eukaryotic cells, there are unique structural differences between animal and plant cells.

Learning Objectives

  • Differentiate between the structures found in animal and plant cells

Key Points

  • Centrosomes and lysosomes are found in animal cells, but do not exist within plant cells.
  • The lysosomes are the animal cell’s “garbage disposal”, while in plant cells the same function takes place in vacuoles.
  • Plant cells have a cell wall, chloroplasts and other specialized plastids, and a large central vacuole, which are not found within animal cells.
  • The cell wall is a rigid covering that protects the cell, provides structural support, and gives shape to the cell.
  • The chloroplasts, found in plant cells, contain a green pigment called chlorophyll, which captures the light energy that drives the reactions of plant photosynthesis.
  • The central vacuole plays a key role in regulating a plant cell’s concentration of water in changing environmental conditions.

Key Terms

  • protist: Any of the eukaryotic unicellular organisms including protozoans, slime molds and some algae; historically grouped into the kingdom Protoctista.
  • autotroph: Any organism that can synthesize its food from inorganic substances, using heat or light as a source of energy
  • heterotroph: an organism that requires an external supply of energy in the form of food, as it cannot synthesize its own

Animal Cells versus Plant Cells

Each eukaryotic cell has a plasma membrane, cytoplasm, a nucleus, ribosomes, mitochondria, peroxisomes, and in some, vacuoles; however, there are some striking differences between animal and plant cells. While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC: a complex called the centrosome. Animal cells each have a centrosome and lysosomes, whereas plant cells do not. Plant cells have a cell wall, chloroplasts and other specialized plastids, and a large central vacuole, whereas animal cells do not.

The Centrosome

The centrosome is a microtubule-organizing center found near the nuclei of animal cells. It contains a pair of centrioles, two structures that lie perpendicular to each other. Each centriole is a cylinder of nine triplets of microtubules. The centrosome (the organelle where all microtubules originate) replicates itself before a cell divides, and the centrioles appear to have some role in pulling the duplicated chromosomes to opposite ends of the dividing cell. However, the exact function of the centrioles in cell division isn’t clear, because cells that have had the centrosome removed can still divide; and plant cells, which lack centrosomes, are capable of cell division.

Lysosomes

Animal cells have another set of organelles not found in plant cells: lysosomes. The lysosomes are the cell’s “garbage disposal.” In plant cells, the digestive processes take place in vacuoles. Enzymes within the lysosomes aid the breakdown of proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles. These enzymes are active at a much lower pH than that of the cytoplasm. Therefore, the pH within lysosomes is more acidic than the pH of the cytoplasm. Many reactions that take place in the cytoplasm could not occur at a low pH, so the advantage of compartmentalizing the eukaryotic cell into organelles is apparent.

The Cell Wall

The cell wall is a rigid covering that protects the cell, provides structural support, and gives shape to the cell. Fungal and protistan cells also have cell walls. While the chief component of prokaryotic cell walls is peptidoglycan, the major organic molecule in the plant cell wall is cellulose, a polysaccharide comprised of glucose units. When you bite into a raw vegetable, like celery, it crunches. That’s because you are tearing the rigid cell walls of the celery cells with your teeth.

Chloroplasts

Like mitochondria, chloroplasts have their own DNA and ribosomes, but chloroplasts have an entirely different function. Chloroplasts are plant cell organelles that carry out photosynthesis. Photosynthesis is the series of reactions that use carbon dioxide, water, and light energy to make glucose and oxygen. This is a major difference between plants and animals; plants (autotrophs) are able to make their own food, like sugars, while animals (heterotrophs) must ingest their food.

Like mitochondria, chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplast’s inner membrane is a set of interconnected and stacked fluid-filled membrane sacs called thylakoids. Each stack of thylakoids is called a granum (plural = grana). The fluid enclosed by the inner membrane that surrounds the grana is called the stroma.

The chloroplasts contain a green pigment called chlorophyll, which captures the light energy that drives the reactions of photosynthesis. Like plant cells, photosynthetic protists also have chloroplasts. Some bacteria perform photosynthesis, but their chlorophyll is not relegated to an organelle.

The Central Vacuole

The central vacuole plays a key role in regulating the cell’s concentration of water in changing environmental conditions. When you forget to water a plant for a few days, it wilts. That’s because as the water concentration in the soil becomes lower than the water concentration in the plant, water moves out of the central vacuoles and cytoplasm. As the central vacuole shrinks, it leaves the cell wall unsupported. This loss of support to the cell walls of plant cells results in the wilted appearance of the plant. The central vacuole also supports the expansion of the cell. When the central vacuole holds more water, the cell gets larger without having to invest a lot of energy in synthesizing new cytoplasm.


Differences Between Plant and Animal Cells

Animal cells and plant cells are similar in that they are both eukaryotic cells. These cells have a true nucleus, which houses DNA and is separated from other cellular structures by a nuclear membrane. Both of these cell types have similar processes for reproduction, which include mitosis and meiosis. Animal and plant cells obtain the energy they need to grow and maintain normal cellular function through the process of cellular respiration. Both of these cell types also contain cell structures known as organelles, which are specialized to perform functions necessary for normal cellular operation. Animal and plant cells have some of the same cell components in common including a nucleus, Golgi complex, endoplasmic reticulum, ribosomes, mitochondria, peroxisomes, cytoskeleton, and cell (plasma) membrane. While animal and plant cells have many common characteristics, they are also different.


Lab 3-Plant and animal cells-Assignment

 Understand basic differences between prokaryotic and eukaryotic cells  Examine, compare and contrast plant and animal cells as examples of the diversity of eukaryotic cell shapes, sizes and functions.

Background Information on Eukaryotic Cells :

The cells found in plant and animals are eukaryotic. They contain a membrane-bound nucleus and

membrane-bound organelles. However, there are structural and functional differences between plant and animal

cells. The purpose of this exercise is for you to make observations on the general characteristics of plant and

animal cells as examples of eukaryotic cells and to note the similarities and differences between both types of

cell s. In last week’s lab exercise, you briefly studied a few examples of unicellular eukaryotes. In this week’s

lab assignment, you will have an opportunity to study eukaryotic cells that come from multicellular organisms. In multicellular organisms, similar eukaryotic cells are grouped together into sheets and masses called tissues

and organs that perform a similar function or functions.

Before continuing your study of eukaryotic cells, it is important to introduce some of the cellular

structures and characteristics you will look for and identify while completing the assignment. As you examine

the images and videos of various cell types, you should compare them in shape , size and intra-cellular

components. Inside eukaryotic cells are small structures called organelles , each with unique structural and

functional characteristics. The following is a list of cell structures and found inside animal cells (plant cells differ in a few instances):

a. The plasma membrane (aka cellular membrane ) forms the outer limiting boundary of the cell and separates contents inside from the external environment.

b. The cytoplasm includes all material within the cell membrane except the nucleus it is made of cytosol and organelles.

c. The organelles are specialized sub-cellular units, miniature organs within cells of sorts, and include: i. nucleus ii. mitochondria iii. endoplasmic reticulum iv. Golgi bodies v. lysosomes vi. ribosomes

d. The cytosol is a gel-like substance mostly made of water and other substances such as ions, ex. sodium [Na+] and potassium ions[K+]. It is the fluid inside organelles and in which the organelles are suspended within the cell.

BIO 10 Intro to Biology Lab

Assignment-Due on D2L in the folder “Plant & Animal Cells” by 05/30 at

11:59PM

Read through the information about plant and animal cells provided in the next few pages, study the

images and videos, and use your textbook from lecture to answer the questions for 15 points. Enter the

answers on this document or create a separate MS Word document. When you’ve answered all

questions, upload the file to the assignment folder “Plant and Animal Cells” under the Assignments tab

on D2L by 05/31 at 11:59 PM

I. EXAMINING PLANT CELLS

Onion Epidermal Cells

Onion (Genus Allium ) has layers of modified leaves, called scales that can be easily separated from one another. Observe the onion cells shown in the 2 images above that are stained with Lugol’s iodine stain (notice the darkly stained nucleus). For a video on how these slides are prepared, visit the following YOUTUBE video: https://www.youtube.com/watch?v=PrX3h-AflZI. The onion epidermis is a tissue. Remember that a tissue is an aggregation of similar cells that are similar in structure and function. The onion epidermal cells are surrounded by a cell membrane and then a cell wall.

Describe the shape of these cells. (1 pt) The general shape of an onion cell is square or rectangular. The interior of the cell is easy to see and focuses well for microscopic observation. Onion cells fit together like pieces of floor tile, which is sort of what you would expect to see in a layering effect.

What do you hypothesize is the function of the cell wall is? (1 pt) The shape of an onion cell is generally rectangle or square because it is easier to build a " brick wall " (cell wall) out of rectangular bricks. Any structure that minimizes interstitial space will hence allow more "life", thus possibly making it stronger.

II. EXAMINING ANIMAL CELLS

Human Epithelial Cells

The inner surface of the mouth is lined with layers of cells aggregated as a tissue. This tissue is called epithelium. Slides of this type of cell can be prepared easily by using the blunt end of a clean toothpick to gently scrape off some epithelial tissue from the inside of your cheek. The contents of the toothpick are then spread on a small area of a clean slide and stained with a methylene blue stain. You can watch a video of how this slide is typically prepared in the lab: https://en.wikipedia.org/wiki/File:Human_Cheek_Epithelial_Cells_- _How_to_Prepare_a_Wet_Mount_Microscope_Slide.webm

Methylene blue is a basic dye that reacts with acidic molecules in the cell to give varying shades of blue.

Which part(s) of the cell has (have) absorbed the greatest amount of stain? (1 pt) (Hint: darkest stained structure)

Why? (see note above the previous question to help you answer this question) (1 pt) Since it is empty it will absorb the color

  1. Look around the image of mouth epithelial cells. You should be able to see very tiny, dark-blue stained dots. Those “dots” are bacterial cells (prokaryotic cells) on top of or around the human’s epithelial cells (eukaryotic cells). How many times bigger is an epithelial cell compared to a bacterium? (1 pt)

Epithelial cell: 25 microns it is 25 time bigger than bacteria Bacterial cell: 0.5 - 1 micron

Blood Cells

Observe the image above of human blood stained with Wright’s stain. It was taken at a similar magnification as the cheek epithelial cells. Most of the cells that you see in blood are small , round , biconcave cells with a pinkish color the look like miniature saucers (shallow dishes) or donut holes. These are called red blood cells , or erythrocytes. These cells are responsible for carrying oxygen to all parts of your body using a protein called hemoglobin that binds to oxygen.

  1. Compare the relative size of a red blood cell with that of a cheek epithelial cell and with a bacterium. Which is the largest? Smallest? (1 pt)

Epithelial cells 25 microns Largest

Red blood cells 7 microns Small

Bacteria 0.5 - 1 micron Smallest

  1. How does the movement of free-living amoebas compare to that of white blood cells in our blood? (1 pt)

Structurally, amoebae closely resemble the cells of higher organisms. "They are like our cells, and in fact when they are moving they look very much like our white blood cells, " Maciver told LiveScience. Like our white blood cells, amoebae move using pseudopodia (which translates to "false feet ")

In the image below, notice that in the spaces between the red and white blood cells, you may see tiny darkly stained structures. These structures which are cell fragments are called platelets , or thrombocytes. They help form blood clots to reduce or stop bleeding, and help wounds heal. Checking the number of platelets in your blood is helpful in diagnosis of certain diseases.

The actual process of blood clot formation is illustrated in this short video: https://medlineplus.gov/ency/anatomyvideos/000011.htm

13.What is the function of platelets? (1 pt)

While the primary function of the platelet is thought to be hemostasis, thrombosis, and wound healing through a complex activation process leading to integrin activation and formation of a “core” and “shell” at the site of injury, other physiological roles for the platelet exist including immunity and communication.

The image of blood shown below is reflective of an inherited blood disorder known as sickle cell anemia. Notice the few crescent-shaped cells among the many normal cells. This shape is clearly not like those of the other saucer-looking red blood cells and is typical of someone with sickle cell anemia. Those red blood cells are crescent or sickle shaped due to a substitution of a single (1) amino acid necessary to build hemoglobin proteins carried inside red blood cells to transport Oxygen throughout the body. Due to the amino acid being substituted for one typically not there, the hemoglobin cannot carry the same amount of oxygen molecules and the cell partly collapses on itself giving it that sickled shape. To learn more about what sickle cell disease is, visit the non-profit Sickle Cell Disease Association of America (https://www.sicklecelldisease.org/sickle-cell- health-and-disease/types/).

  1. What are some of the possible disadvantages for someone not producing all of his/her red blood cells with ‘normal’ hemoglobin? (1pt)

Low hemoglobin levels lead to anemia, which causes symptoms like fatigue and trouble breathing.


4.3E: Comparing Plant and Animal Cells - Biology

Part 1: Observing Plant Cells

1. Obtain a piece of onion and use forceps to peel the membrane from the underside of the onion. This will appear very thin and mostly transparent.
2. Place the membrane flat on the slide and use your forceps to spread it out, avoid having any folds in the membrane.
3. Place a drop of iodine on the membrane. (Caution: iodine will stain skin and clothes too!)
4. Carefully place a cover slip over the specimen.

View the microscope with scanning, low and high power objectives. You may need to review the steps of using the microscope. Draw your cells as they appear in the viewing field. On the 400x image, label the cell wall, nucleus, and cytoplasm.

Part 1: Observing Animal Cells

1. Clean the slide you created with the onion by rinsing and drying it. Throw the cover slip away.
2. Put a drop of methylene blue or other stain on the slide.
3.Gently scrape the inside of your cheek with the flat side of a toothpick and stir the end of the toothpick into the stain to create a smear.
4. Place a coverslip onto the slide. (Cover slips are small, thin, square plastic or glass pieces).

Draw your cells as they appear in the viewing field. On the 400x image, label the cell wall, nucleus, and cytoplasm.

Analysis

1. Describe two ways in which the plant and animal cells are similar based on your observations.

2. Describe two ways in which they are different based on your observations.

3. Consider that there are many organelles and structures of the cell that were not visible using the light microscope. List two organelles that might have been visible if you were using a microscope that had a greater magnification.

4. In both cases, a stain was used in the preparation of the slide. Why do you think staining is necessary?

5. Create a Venn diagram that shows how plant and animal cells are different and the same. You should include information from your notes or textbook (not just observations from this lab.)

/>This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.


Q&A: frequently asked questions are quickly answered here

What do plant cells have, but animal cells do not?

In brief, the most striking difference between animal cells and plant cells is that plant cells have three unique organelles: central vacuole, cell wall, and chloroplast.

What do animal cells have, but plant cells do not?

Animal cells have centrioles/centrosomes that most plant cells don’t. Some animal cells also have flagella and cilia, which are absent in plant cells.

What does a plant cell look like?

Due to the cell wall, many plant cells have a rectangular fixed shape.

[in this figure] The illustration of the cell wall.
The cell wall acts like a cardboard box that protects the soft cell membrane and cytoplasm. Like real cardboard boxes can be piled up to build a tall wall, the plant grows by adding cells one by one as living building blocks. The weight is loaded primarily on the structural cell walls.

Do plant cells have cell membranes?

Yes, plant cells have a layer of cell membrane underneath the cell wall. The cell membrane detaches from the cell wall under a hypertonic condition.

[In this figure] Turgor pressure on plant cells diagram.
Photo source: wiki.

Do plant cells have mitochondria?

Yes, both animal and plant cells have mitochondria, but only plant cells have chloroplasts. In plant cells, chloroplasts absorb energy from sunlight and store it in the form of sugar (a process called photosynthesis). In contrast, mitochondria use chemical energy stored in sugars as fuels to generate ATP (called cellular respiration). Like animal cells, plant cells use ATP to drive other cellular activities.

[In this figure] The carbon cycle showing how energy flows between chloroplasts and mitochondria to benefit the ecosystem.

Do animal cells have a cell wall?

No, animal cells do not have a cell wall so they can freely change their cell shapes.

Do plant cells have centrioles?

No, plant cells do not have centrioles for their mitosis except for some lower plant forms.

Do plants have lysosomes?

The presence of lysosomes in plant cells is under debate. Vacuoles in plant cells can fulfill the role of the animal lysosomes.

Do plant cells have ribosomes?

Yes, plant cells have both free and rough endoplasmic reticulum-bound ribosomes for protein synthesis.

What do all cells have in common?

All cells (prokaryotic or eukaryotic animal or plant) share four common components: (1) Plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment

(2) Cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found

(3) DNA, the genetic material of the cell

(4) Ribosomes, particles that synthesize proteins.

All cells on Earth have similar chemical compositions and meet the description of cell theory. The central dogma of molecular biology as “DNA makes RNA, and RNA makes protein” is also true in all cells.

Are plants eukaryotic?

Yes, both plants and animals are eukaryotes and have membrane-bound nuclei and organelles. Prokaryotic cells are bacteria or archaea.

Do animal cells have chloroplasts?

No, animals do not have chloroplasts, so they can not produce their food. However, some animals may borrow chloroplasts and live like a plant. Elysia chlorotica (common name the eastern emerald elysia) is one of the “solar-powered sea slugs,” utilizing solar energy to generate energy. The sea slug eats and steals chloroplasts from the alga Vaucheria litorea. The sea slugs then incorporate the chloroplasts into their own digestive cells, where the chloroplasts continue to photosynthesize for up to nine months.

[In this figure] Elysia cholorotica, a sea slug found off the U.S. East Coast, can steal photosynthetic chloroplasts from algae.
Photo source: Mary S. Tyler/PNAS

Do plant cells have cytoskeleton?

Yes, both plant and animal cells have a similar cytoskeleton. Constrained by the cell wall, the plant cell’s cytoskeleton does not allow a dramatic change of the cell shape. However, the cytoskeleton network of protein filaments, microtubules, and interconnecting filamentous bridges generate shape, structure, and organization to the cytoplasm of the plant cell. The cytoskeleton also drives the cytoplasmic streaming in plant cells.

How does cytokinesis differ in plant and animal cells?

Cytokinesis occurs in mitosis and meiosis for both plant and animal to separate the parent cell from daughter cells.

In plants, cytokinesis occurs when a cell wall forms in between the daughter cells. In animals, cytokinesis occurs when a cleavage furrow forms. This pinches the cell in half.

[In this figure] The difference of cytokinesis in plant and animal cells.