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Chapter 34: Problem 57

What determines whether a zygote will undergo total or partial cleavage? a. Total cleavage takes place in eggs having a large amount of yolk, whereas partial cleavage occurs in eggs having very little or no yolk. b. Total cleavage occurs when eggs possess equal concentration of yolk at both poles, whereas partial cleavage occurs when the yolk is not equally distributed. c. Total cleavage takes place in eggs having little or no yolk, whereas partial cleavage occurs in eggs having a large amount of yolk. d. Total cleavage occurs when divisions of the blastomeres are separate, whereas partial cleavage occurs when blastomeres stay partially connected.

Short Answer

Expert verified
Option c.

Step by step solution

01

- Understanding the concepts

First, understand what total and partial cleavage mean: Total cleavage (holoblastic cleavage) occurs when the entire zygote divides, typically happening in eggs with minimal yolk. Partial cleavage (meroblastic cleavage) occurs when only part of the zygote divides, typically occurring in eggs with a large amount of yolk.
02

- Analyze option a

Option a states that total cleavage takes place in eggs with a large amount of yolk, and partial cleavage occurs in eggs having very little or no yolk. This is incorrect as total cleavage happens in eggs with little yolk.
03

- Analyze option b

Option b suggests that total cleavage occurs when there is an equal concentration of yolk, and partial cleavage when yolk is not equally distributed. This also does not align with the concept as total cleavage does not depend on equal yolk distribution.
04

- Analyze option c

Option c states that total cleavage occurs in eggs with little or no yolk, whereas partial cleavage occurs in eggs with a large amount of yolk. This correctly describes the relationship between yolk amount and type of cleavage.
05

- Analyze option d

Option d suggests that total cleavage happens with separate blastomere divisions, while partial cleavage occurs when blastomeres stay connected. This description does not accurately define total and partial cleavage in terms of yolk.
06

- Conclusion

Based on the analysis, option c is the correct choice as it correctly explains that total cleavage occurs in eggs with little or no yolk and partial cleavage occurs in eggs with a large amount of yolk.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Holoblastic Cleavage
When the entire zygote divides during embryonic development, it is known as holoblastic cleavage. This type of cleavage occurs in eggs that have little or no yolk. The small amount of yolk allows the entire cell to divide completely. Holoblastic cleavage is typical in organisms such as:
  • Humans
  • Frogs
  • Sea urchins
For example, in human eggs, which contain minimal yolk, the zygote undergoes complete division. Each round of division produces increasingly smaller cells called blastomeres.
Meroblastic Cleavage
Meroblastic cleavage occurs when only a part of the zygote divides. This happens in eggs that have a significant amount of yolk, making complete division impractical. The large amount of yolk impedes the ability of the cell to divide entirely. Instead, only the area without yolk undergoes division. This type of cleavage is observed in species like:
  • Birds
  • Reptiles
  • Fish
In chicken eggs, for instance, the cleavage is limited to a small disc of cytoplasm on top of the yolk, known as the blastodisc.
Yolk Distribution in Eggs
Yolk distribution plays a crucial role in determining the pattern of cleavage in developing eggs. The amount and placement of yolk can vary significantly among different species. Generally, eggs are categorized based on yolk distribution as:
  • Isolecithal: Evenly distributed yolk, leading to holoblastic cleavage.
  • Mesolecithal: Moderate and uneven yolk distribution, still typically results in holoblastic cleavage.
  • Telolecithal: Dense yolk concentrated at one end, resulting in meroblastic cleavage.
Understanding the yolk distribution helps explain why certain animals undergo different cleavage patterns during embryogenesis.
Blastomeres
Blastomeres are the smaller cells produced by the division of the zygote during cleavage. The type of cleavage, whether holoblastic or meroblastic, influences the characteristics of these blastomeres. In holoblastic cleavage, each division produces blastomeres that are of approximately equal size. These cells subsequently form a structure called a blastula. In meroblastic cleavage, however, the divisions result in an uneven distribution of blastomeres due to the presence of a large yolk. The blastomeres form a layer around the yolk. The study of blastomeres is essential for understanding early developmental stages in various organisms.

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Most popular questions from this chapter

Why is sexual reproduction useful when only half the individuals reproduce and two cells must combine to form a new cell? a. It completes in a very short period of time. b. It results in the rapid production of many offspring. c. It increases genetic diversity, allowing organisms to survive in an unpredictable environment. d. It requires less energy and leads to genetic variation in the offspring.

Compare the specialization of reproductive structures found in different types of land animals. a. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the testes and sperm maturing in the ovaries. b. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the ovaries and sperm maturing in the testes. c. In birds, sperm are transferred via the spermatheca, whereas in mammals, the presence of the penis and vagina allows direct delivery. Complete reproductive systems are formed in insects, with eggs maturing in the ovaries and sperm maturing in the testes. d. In birds, an opening called the cloaca is used to transfer sperm, whereas in mammals, the presence of the penis and vagina allows direct delivery. Insects always use parthenogenesis.

What is the nature of the oogonium and the secondary oocyte? Which process results in the formation of the secondary oocyte? a. A diploid oogonium forms a haploid oocyte by the process of mitosis. b. A haploid oogonium forms a diploid oocyte by the process of meiosis. c. A diploid oogonium forms a haploid oocyte by the process of meiosis. d. A haploid oogonium forms a haploid haploid oocyte by the process of meiosis.

Which method of reproduction produces identical offspring and is most successful in a stable environment? a. asexual reproduction b. sexual c. conjugation d. inbreeding

How does the feedback mechanism of hormones lead to muscular contractions during labor? a. A feedback relay occurs between the uterus, hypothalamus, and posterior pituitary to assure an adequate supply of oxytocin, which causes the contraction of smooth muscles of the uterus, leading to the birth of the baby. b. The posterior pituitary continuously produces oxytocin, which is sufficient for muscular contraction in the uterus, thereby causing the birth of the baby. c. A feedback relay occurs between the uterus, hypothalamus, and posterior pituitary to assure an adequate supply of prolactin, which causes the contraction of the smooth muscles of the uterus, leading to the birth of the baby. d. A feedback relay occurs between the uterus, hypothalamus, and posterior pituitary to assure an adequate supply of progesterone, which causes the contraction of the smooth muscles of the uterus, leading to the birth of the baby.
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