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Práctica de Laboratorio 4

Observación de la mitosis en raíz de cebolla
Introducción

La división celular es solo una pequeña parte del ciclo de crecimiento y reproducción llamado ciclo celular. En general, las células recién formadas toman nutrimentos de su ambiente, sintetizan más componentes celulares y aumentan de tamaño. Al cabo de un lapso de tiempo que puede variar, según la especie de organismo que se trate, el tipo de célula y de nutrimentos disponibles, la célula se divide. Este proceso se denomina mitosis. Para fines de estudio, los científicos dividieron la mitosis en cuatro fases, tomando en cuenta el aspecto y el comportamiento de los cromosomas: (1) profase, (2) metafase, (3) anafase y (4) telofase. Recuerda que estas fases no son acontecimientos independientes, sino que forman un evento continuo, en el que cada fase se funde con la siguiente.

En esta práctica observaras preparaciones permanentes de cortes de raíz de la cebolla con el propósito de observar las diferentes fases de la mitosis.
Problema

¿Qué tan sencilla puede ser la observación y posterior identificación de las fases de la mitosis en vegetales?
Discusión previa

  1. Que es la mitosis?

____________________________________________________________________________________________________________________________________________________________

  1. ¿Porque es importante la mitosis?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

  1. Si observas una célula viva al microscopio y en ella distingues cromosomas alineados en el plano ecuatorial de la célula, a que etapa de la mitosis corresponde?

______________________________________________________________________________

  1. ¿En el ser humano que tipo de células se dividen por mitosis?

______________________________________________________________________________

  1. ¿La mitosis está relacionada con la reproducción sexual o asexual? ¿Por qué?

______________________________________________________________________________

______________________________________________________________________________


Procedimiento

  1. Los asistentes de laboratorio te proporcionaran una laminilla que utilizarás para observarla al microscopio.




  1. Debes enfocar utilizando la técnica de enfoque que aprendiste en la primer sesión de laboratorio (sigue los pasos para evitar accidentes).




  1. Una vez enfocada la muestra busca cada una de las fases de la mitosis y elabora un dibujo de la fase que observas.




  1. Explora diferentes campos dentro de la misma muestra en busca de otras fases.




  1. Intercambia tu laminilla con otro compañero y repite el procedimiento.


Análisis y Conclusiones

  1. ¿Cuántas células con fases mitóticas pudiste observar en un solo campo a 40X?

________________________________________________________________

  1. ¿Cual fase fue la que encontraste con mayor facilidad? ¿Por qué?

________________________________________________________________

  1. ¿Aproximadamente cuantas células se observan por campo en 40X?

________________________________________________________________

  1. ¿Qué dificultades encontraste en esta práctica de laboratorio?

____________________________________________________________________________________________________________________________________________________________

  1. ¿Por qué se utilizaron células de la raíz para observar la mitosis?

____________________________________________________________________________________________________________________________________________________________

Session 1

Instructions: Continue with Chapter Assessment 7


  1. Infer. Would you expect skin cells to contain more or fewer mitochondria than muscle cells? Explain your answer.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


  1. Infer. Pacemakers are devices that help keep heart muscle cells contracting at a steady rate. If a person needs a pacemaker, what does the suggest about his or her heart cells’ ability to send and receive chemical messages?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



Cell Size

Cell

Approximate Diameter

Escherichia coli (bacterium)

0.5- 0.8 µm

Human erythrocyte (red blood cell)

6-8 µm

Human ovum (egg cell)

100µm

Saccharomyces cervisiae (yeast)

5-10 µm

Streptococcus pneumoniae (bacterium)

0.5- 1.3 µm




  1. Classify. Classify each of the cells listed as prokaryotes and eukaryotes.

____________________________________________________________________________________________________________________________________________________________________



  1. Compare and contrast. Compare the size of the prokaryotic cells and eukaryotic cells.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


  1. Infer. Chlamydomonas reinhardtii is a single celled organism with an approximate diameter of 10µm. Is it more likely a prokaryotic or eukaryotic organism? Explain your answer.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________


  1. Persuasion. Different beverages have different concentrations of solutes. Some beverages have low solute concentrations and can be a source of water for body cells. Other beverages have high solute concentrations and can actually dehydrate your body cells. Should companies that market high- solute drinks say that the drink quench thirst?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

  1. What is the relationship between active transport and homeostasis? Give one example of active transport in an organism, and explain how the organism uses energy to maintain homeostasis.

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Most materials entering the cell pass across the cell membrane by diffusion. In general, the larger the molecule, the slower the molecule diffuses across the membrane. The graph shows the size of several molecules that can diffuse across a lipid bilayer.

mlbio10a1270.png

  1. Calculate. By approximately what percentage is a molecule of carbon dioxide smaller than a molecule of glucose?

  1. 24%

  2. 50%

  3. 75%

  4. 100%




  1. Formulate Hypotheses. Which of the following is a logical hypothesis based on the graph shown?

  1. Cells contain more glucose than oxygen.

  2. Oxygen molecules diffuse across the cell membrane faster than water molecules.

  3. Glucose molecules must cross the cell membrane by active transport.

  4. Carbon dioxide crosses the cell membrane faster than glucose.


Session 2

Objective: Get ready for your test practicing with the following standardized test prep.

Instructions: Answer the following standardized test prep.
STANDARDIZED TEST PREP


  1. Animal cells have all of the following EXCEPT

  1. Mitochondria

  2. Chloroplasts

  3. A nucleus

  4. A cell membrane




  1. The nucleus includes all of the following structure Except

  1. Cytoplasm

  2. A nuclear envelope

  3. DNA

  4. A nucleolus




  1. The human brain is an example of a(n)

  1. Cell

  2. Tissue

  3. Organ

  4. Organ system




  1. Which cell structures are sometimes found attached to the endoplasmic reticulum?

  1. Chloroplasts

  2. Nuclei

  3. Mitochondria

  4. Ribosomes




  1. Which process always involves the movement of materials from inside the cell to outside the cell?

  1. Phagocytosis

  2. Exocytosis

  3. Endocytosis

  4. Osmosis




  1. Which of the following is an example of active transport?

  1. Facilitated diffusion

  2. Osmosis

  3. Diffusion

  4. Endocytosis




  1. The difference between prokaryotic and eukaryotic cells involves the presence of

  1. A nucleus

  2. Genetic material in the form of DNA

  3. Chloroplasts

  4. A cell membrane




  1. In this experiment, sucrose probably entered the cells by means of

  1. Endocytosis

  2. Phagocytosis

  3. Osmosis

  4. Active transport




  1. The graph shows that as the concentration of sucrose increased from 10 to 30 mmol/L, the plant cells

  1. Took in sucrose more slowly

  2. Took in sucrose more quickly

  3. Failed to take in more sucrose

  4. Secreted sucrose more slowly




  1. Based on the graph, the rate of sucrose uptake

  1. Increased at a constant rate from 0 to 30 mmol/L

  2. Decreased at varying rates from 0 to 30 mmol/L

  3. Was less at 25 mmol/L than at 5 mmol/L

  4. Was constant between 30 and 40 mmol/L



  1. What would you expect to happen if you placed a typical cell in fresh water?

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Session 3

Objective: Review all of the concepts seen in chapter 7.

Instruction: Answer correctly workbook 7-1 and 7-2
7.1 Life Is Cellular

Lesson Objectives

State the cell theory.

Describe how the different types of microscopes work.

Distinguish between prokaryotes and eukaryotes.

Lesson Summary

The Discovery of the Cell The invention of the microscope in the 1600s enabled researchers to see cells for the first time.

Robert Hooke named the empty chambers he observed in cork “cells.”

Anton van Leeuwenhoek was the first to observe living microorganisms.

Cells are the basic units of life.

Discoveries by German scientists Schleiden, Schwann, and Virchow led to the development of the cell theory, which states:

  • All living things are made of cells.

  • Cells are the basic units of structure and function in living things.

  • New cells are produced from existing cells.


Exploring the Cell Scientists use light microscopes and electron microscopes to explore the structure of cells.

Compound light microscopes have lenses that focus light. They magnify objects by up to 1000 times. Chemical stains and fluorescent dyes make cell structures easier to see.

Electron microscopes use beams of electrons focused by magnetic fields. They offer much higher resolution than light microscopes. There are two main types of electron microscopes—transmission and scanning. Scientists use computers to add color to electron micrographs, which are photos of objects seen through a microscope.
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